Yes, you can stop or vary your payments during a tax year. However, if you do not make a payment in the whole of a tax year, and you want to start paying in again the following year, you will have to make a new application or complete a 'top-up' application form.
If you stop paying monthly subscriptions, the policy will continue. However, in the first 12 months, you need to maintain a minimum premium of at least £30 per month for the policy to remain open, unless any other lump sums are added to take the capital invested to over £300.