I have a Chinese Elm now which I'm planning to keep as an indoor bonsai. Even after all research I'm stuck on where to position it in summer. On forums its say things such as let it stay outside for summer (but I want it indoor) and not to put in on a windowsill in summer as leaves burn. Any idea where I can put it for summer ( I live UK and I'm a complete beginner studying a few books)?

Thanks in advance!

First and best location is outside (Actually, they can stay outside except for long deep frosts)
If you do not have that option, you could keep it inside, but then in the unniest & best ventilated location you have.
Leaves burn because they are not used to direct sun. Not because they receive sun. So you need to make sure the tree does not move from a dark room into full sun directly.