Can anyone suggest a holiday destination up to 2 hours flight from London that's likely to have sunshine in last week of Sept? A nice hotel with a big pool would be good too
I would second Mallorca. This is a good time to visit and it won't be so busy as in July, August and the pools and sea will have warmed up nicely in the months before. Really depends on what you want from your holiday to recommend a place to stay as there are so many different areas to choose from all with things going for or against them depending on your taste.
I went to Sorrento two years running in September and it was wonderful. Stunning scenery, the best food I have ever had, and plenty to do. I can't recommend the Bay of Naples area highly enough.
I'm a massive fan of the Balearics (well Menorca anyway) but it depends how critical sun and heat are. The end of September can be changeable, for more guaranteed sun and that flying distance you might want to look at Southern Spain (Costa del Sol).