I assume, then, that it is an indoor bonsai? The leaves that are going yellow seem to be the older ones. This is normal. The rest of it looks very healthy. This could probably do with getting a bit more light, but not hot direct sunlight once the srength of the sun warms up. You may need to rotate it from thjis position to the window every few days. It may also appreciate being sprayed with water. It's a lovely thing, don't recognise it.Could you contact the supplier to see if they know what sort it is?

The leaves look very much like a rubber plant or something in the Ficus family. I didn't know they could be bonsai'ed but your plant looks very good. Although it's still quite cool, have you checked the undersides of the yellow leaves for red spider mite as this can be a problem on anything grown in dry, warm conditions?

If you bought it from a garden centre I am sure they will be only too pleased to help you. Lots of bonsai do not like too hot a room and will quite happily sit outside in shelter year round. It is stunning and looks to be quite old. If the GC is too far away to return to for advice I have found growers and specialists are very sympathetic to questions if you e mail them a photograph. I thought it looks a bit like a lemon or orange tree but I do not know enough to give you a definitive answer.

Thank you all for your quick responses... I've checked the leaves and thankfully no red spider mite. Perhaps it is just shedding its old leaves!!! I'll give it a spray and keep my eye on it! :-)

Any further thoughts on what the tree is are greatly recieved!!!

How does the temperature in your room compare to that in the GC. Often they are unheated.

It's in the kitchen/diner which is a large open room with only one radiator at the other side of the room, I personally find it quite a cool room, although it's difficult to remember what it is like comapred to the garden centre! The garden centre is about 20 odd miles away, so I haven't been by recently, but I shall take my photos there next time I'm passing by for their opinion too!!

They should be able to tell you what the plant is, too - it is indeed very nice, and I'd quite like to know what it is as well.

Keep us posted please

Take a look at this photo of a Ficus bonsai.
http://www.usaflorist.com/large/W-403.jpg
I'd say that's very similar if not identical to what you have. The yellowing leaves fit the type too.

I just bought a bonsai ficus.... though the instructions said to keep it indoors I did the opposite. It is now outdoors because i have a cheeky 3 year old who may just not let it be. Do you think this is right or will it grow wild - this being the warm tropics where I live.

Looks like a type of Ficus with the Banyan type of roots. I have a Jinseng Ficus that has some of those types of roots but the trunk is bulbous. I have it outside on our patio now in the good weather but they are cold and frost sensitive so it lives indoors though out the winter and early spring months. They are a good medium light plant. Our patio is covered, (slatted diffused light) and faces east. Very nice Bonsai!

Safina, Because you live in the tropics outside is fine but the growing wild is up to you to control. I think many people think that when they buy a Bonsai all they have to do is water, feed and generally just keep it alive. Nothing could be farther from the truth. They will continue to put out new growth and if left alone they will lose their shape completely. Shaping is what the art of Bonsai is all about, otherwise all you wind up with is a plant in a small pot. You must study your Bonsai and shape according to your taste. It is live sculpting. If for example you have a space on the trunk that you want to fill and you are fortunate to have the plant start shooting from that place, leave it alone and let it grow. If you have an area that is getting too full or long shape that place. I will sit and study mine and if I see some growth that is interfering with the shape I will snip or pinch it off. Also turn your plant around. There will be a front and a back. The front being the most pleasing view. Sometimes I will notice an area that I am not sure of, trimming wise, so I will leave it alone. I may trim it or not. You have to look at the whole picture and consider where you want to go with this plant or if you are satisfied with the final product you just have to occasionally "clean" up the shape and enjoy.

Sprngrboy has made a good point - you should sit and look at your tree, not stand, when deciding if it needs shaping. Our gardening club members enjoyed a very informative talk on the art of Bonsai. I did a blog on 29th Nov.2012, if you want to check it out.

Excellent answers.
To me this looks like a Ficus bangladensis. and is an indoor bonsai in England but likes to be outside in a semi to shaded area during the warm/hot summer times (here in England).
Can be susceptable to draughts, doesn't like to be moved too often.
Yellowing leaves could be old leaves. Too wet compost. draughts.
If grown on a windowsill inside, take it out of the windowsill as the sun goes down as it's a LOT cooler there than the rest of the room (put your hand near the window at night to test this theory).