I can't tell what plant it is from this distance - any chance of a close up of the leaves? If the plant used for bonsai is normally an outdoor plant, then it should be outdoors for most of the year, the exception being really cold spells or extra shade in hot weather.

Very hard to tell....could be one of the Zelkova's.

Sorry to be the bearer of bad news but these kind of Bonsai do not do very well indoors. Most of the trees you get from the supermarket or DIY shop are not hardy so will not survive outside but they will hate the warmth and the dull conditions indoors.

They're best kept in a cool, frost free porch or conservatory which doesn't get direct sun....not too much to ask lol. Once the risk of frost has passed, it can go outside in a semi shaded area.

Let it dry out slightly in winter but you might be watering it 2 or 3 times a day when its hot.

Chinese elm probably, very popular for bonsai.

This was stated as an indoor Bonsai and I have been keeping it in the enclosed porch where it is pretty cool. The leaves are tiny - probably about 8mm in length, oval shaped and quite shiny. I will try to get a close up photo of one of them when I get the chance.
What should I feed it with and should this not be done until the Spring?

Yep, it's a Chinese Elm. It's semi-deciduous in the winter, especially under cool conditions, so lots of yellow leaves are normal, now. As an indoor plant, it needs extreme light, so try to keep it where the sun can shine on it. Sometime in February or early March, depending on the temperature, it will start to sprout new leaves, and that's when you start to feed. I would use a good houseplant food, at normal frequency, but only half strength--you want to keep it healthy, but not pushing too much growth.

Thank you so much to the people who have answered my query. You have been most helpful.

www.bargainbonsai.co.uk has a section on how to care for this particular bonsai - it is better off outdoors year round, but you can't do that now in the midst of winter - best to acclimatise it in the spring by hardening it off and then leaving outside. You can bring it in for winter, but have a read of that care sheet. If you google 'chinese elm bonsai care' it should come up as one of the options.

Thank you again, Bamboo, - very interesting reading. I shall certainly have a go at leaving it outside starting in the Spring. I live in the north of England, however, so I'm not too sure about it's survival if we get a really hard Winter in 2015. Will have to play it by ear!