Easy to grow chilli plants in England?

I don't know about that particular plant but it's only worth overwintering them if you can give them enough light and warmth. In my opinion, if the temp is going to regularly drop below 60F it's not worth it. When I first started overwintering them I used to bring them into the lounge which was always a lot warmer than that. I, also, was able to put them near the french doors which face south so they got almost as much light as they would outside (needed to turn them round each week to stop them leaning towards the light).

The first plants that we overwintered lasted five years. In those good conditions they continued to give us chillies throughout the winter and I gave them a final pruning back in Feb. By the end of April they were back into producing a lot of new leaves and were in flower by May. By the end of their fifth year they weren't so prolific but years two and three were superb.

Nowadays we just leave them in the propagator in the greenhouse where they are subject to lower temps (mid to upper 50's but with bottom heat and a bit of plastic over the top) but more light. They tend to be a bit more neglected that way but they produce until late into the year, go dormant and still start reasonably early the next year.

 

Nice picture

The amount we picked won't last long. I prefer my chillies fresh and eat about three per day (they're very hot) and Mrs Shiney has preserved a batch of them.

Keeping it on the windowsill is OK for light but it depends on whether you get cold downdrafts at night (or in very cold weather). It may be better to move it away from the window each night. Have it in a good plant saucer and only water it from the bottom. Otherwise you might get fungus gnats (look like vinegar flies) http://www.ext.colostate.edu/pubs/insect/05584.html
If you do need to water the surface I would be inclined to remove the top half inch of soil once a month and replace with fresh compost. Remove all dead leaves that drop on the soil.

If it really likes the conditions it's in it will still drop leaves but also continue to produce new ones. If it doesn't produce new ones don't worry. They start to gorw in early spring.