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CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the §371 National Stage Entry of International Application PCT/IB2013/055428, filed on Jul. 2, 2013, which claims the benefit of United Kingdom Patent Application Serial No. GB 1212092.9, filed on Jul. 6, 2012, the contents of which applications are herein incorporated by reference in their entirety. 
     FIELD OF THE INVENTION 
     This invention relates to collapsible ladders and more specifically to increasing the stability of a extendible ladders when erected. 
     BACKGROUND OF THE INVENTION 
     Collapsible ladders are utilised because of the convenience they provide. They may be transported easily, such as in the trunk of a car, and may be carried and erected by one man. It is beneficial for such ladders to collapse to the smallest possible size, whilst still allowing them to be erected to a useful height. 
     Reducing the physical dimensions to produce the smallest collapsed size has the downside of reducing the width of the footprint when the ladder is erected. A narrower footprint reduces the stability of the ladder, the degree of instability being more noticable the taller the ladder. 
     Previous solutions to this include the provision of removable feet located at the bottom of each stile which serve to widen the foot print of the ladder, but these are cumbersome to attach or remove each time the ladder is collapsed or erected for transport. 
     SUMMARY OF THE INVENTION 
     With a view to mitigating the foregoing disadvantage, the present invention provides an improved extendable ladder. According to an embodiment of the present invention, an extendable ladder has a collapsed mode and an extended mode. When the ladder is transformed from the collapsed mode to the extended mode, at least one ground stabiliser extends laterally from the ladder to widen the footprint of the ladder. 
     Preferably, the stiles of the ladder may extend telescopically. 
     The at least one one ground stabiliser may be urged laterally outwards by a spring. 
     The at least one ground stabiliser may be retained in a retracted position by a pin engaged within a hole when the ladder is in a collapsed mode. 
     The pin may be resiliently biased towards the hole in the ground stabiliser. 
     The pin may be supported by one of the telescopic stiles of the ladder such that when the stiles slide relative to one another as the ladder is extended the pin is pulled out of the hole, releasing the ground stabiliser. 
     Preferably, at least two ground stabilisers may extend coaxially from each of the two stiles of the ladder. 
     The two ground stabilisers may extend from a hollow floor rung and are biased apart by a spring contained within the rung. 
     Preferably the motion of the ground stabiliser is damped. 
     Alternatively a podium may be provided comprising a rectangular platform and a ladder as described above, hingedly attached to each of two opposing sides of the platform. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described further by way of example with reference to the accompanying drawings in which: 
         FIG. 1  shows a sectional view of the lower most rung of a collapsed ladder embodying the present invention, with its ground stabilsers in a retracted position, and 
         FIG. 2  shows a sectional view of the lower most rung of a partially extended extended ladder embodying the present invention, with its ground stabilsers in an extended position. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Turning now to  FIG. 1 , a collapsible ladder embodying the present invention is shown. In this example a telescopic ladder  10  is of the type described in U.S. Pat. No. 5,495,915. The dotted line to the right of the figures represents a vertical line of symmetry. The description provided here should be assumed to be duplicated about this line. 
     The ladder is formed of individual rungs  12 ,  20  having two ends (one end  14  of each rung shown). Each end  14  is connected to and associated with a corresponding hollow stile section  16 . The stile sections  16  associated with a first rung  12  are larger in diameter than the stile sections  18  associated with a second rung  20  immediately above. As a result, the ladder  10  may be collapsed by sliding the stile sections  16 , 18  inside one another resulting in the collapsed ladder having rungs  12 , 20  which rest directly on top of one another. 
     To extend the ladder the rungs  12 , 20  are separated causing the stile sections  16 , 18  to slide telescopically apart. They continue to slide until a spring biased pin  22 , 24  arranged inside the ends  14 , 26  of each rung  12 , 20  engages with a hole  28 , 30  in the circumference of the stile section of the rung immediately above. 
     The spring biased pins  22 , 24  lock the stile sections  16 , 18  at the separation predetermined by the position of the holes  28 , 30 . Typically the rungs are separated starting with the bottom two rungs  12 , 20  and then working up the ladder  10  towards its top. This allows the height of the ladder to be chosen depending on the extension required. 
     As stability is increased by widening the foot print of the ladder, or increasing the distance between the outermost points of the foot of the ladder, the present invention is provided with extendable feet or ground stabilisers  32 . 
     These protrude at the outer circumference of the stiles  34  of the ladder where they meet the floor  36 . The stiles  32  are each provided with a curved high grip rubber foot  38  inserted into the hollow stile  32  to provide a better purchase on the ground  36  regardless of the angle of the ladder  10 . These feet define the width of the foot print of a standard ladder. 
     In the present invention, the ground stabilisers  32  may themselves be in either a retracted ( FIG. 1 ) or extended ( FIG. 2 ) position. In the retracted position, the ground stabilisers of the preferred embodiment increase the width of the foot print of ladder in the preferred embodiment, when compared to a ladder not so equipped. In some applications this may be undesirable and so is considered optional. 
     In an alternative embodiment, the ground stabilisers  32  may be integral to the outer circumference of the stiles  34  immediately adjacent the ground  36  such that when retracted the ground stabilisers  32  sit flush with the circumference of the largest diameter stile portion at the foot of the ladder. 
     For ease of transportation, the ground stabilisers  32  are best maintained in the retracted position as shown in  FIG. 1 . The stabilisers each consist of a cylindrical support tube  40  supported for axial movement within a transverse aperture  42  in the lowermost stile section  16 . In an alternative embdiment, the stabiliser  32  may be supported within a plastic attachment including a foot portion to be attached the bottom of each stile  34 . In this preferred embodiment, the apertures for supporting each tube  40  of each ground stabiliser are coaxial and joined by a hollow ground tube  44 . 
     The stabilisers  32  are urged outwards by means of a resilient member  46  such as a spring acting between the inner most ends  48  of both ground stabilisers  32 . The resilient member  46  is retained within the hollow ground tube  44  running at almost ground level between the stiles  34 . It is raised slightly from the ground to allow the ladder to be used on uneven ground without the ladder  10  rocking on the ground tube  44 . 
     The ground stabilisers  32  are retained in their retracted position against the force of the resilient member  46  in a similar manner to the way in which the stiles of the ladder are locked in the ladder&#39;s extended position. The support tube  40  of each ground stabiliser  32  is provided with a hole  50  in the upper most section of its circumference such that each is aligned with the axis of the respective stile  34 . 
     A resiliently biased pin  52  extending from stile section  18  of rung  20 , mates with the hole  50  preventing the resilient member  46  from forcing the ground stabiliser  32  outwards. 
     When the ladder is extended ( FIG. 2 ) and the rungs ( 12 , 20 ) separated, the stile section  18  carrying the resiliently biased pin  52  is moved upwards and clear of the hole  50  causing the ground stabilisers  32  to extend laterally.

Summary:
An extendable ladder having a collapsed mode and an extended mode, characterized in that when the ladder is transformed from the collapsed mode to the extended mode, at least one ground stabilizer extends laterally from the ladder to widen the footprint of the ladder.