So always ask the issuing agent or airline to confirm that the taxes are included, and to let you know the total. You will be horrified by how much cost this adds to your ticket. I live in Rome, and my brother lives in London. I notice that his airfare to Rome costs far less than mine from Rome to London. Unfortunately it is not possible to buy a discounted ticket in the UK, say to travel from Rome to London and then back to Rome.
Airlines usually make sure that any discounted tickets sold in the UK are only for UK departures.
In the not too distant future, it is likely that some of our advertisers will have offices in continental Europe, and therefore might be able to quote discounted prices for departures from non-UK countries. Unfortunately this is very often true. We try to persuade them either to answer their email promptly, or not to offer it at all. To be a little bit fair to them, if they do offer email, they get inundated. However, they should not be offering a service, if they cannot fulfill it, so please send us an email about persistent offenders.