One thing that wasn't mentioned was the chest x-ray. If you have a longer than 6 month visa, and if you are a citizen of certain countries (I'm pretty sure the sub-continent would be included), you need to go through a (NHS?) health checkup before getting to immigration. Friends of mine have reported that there are long queues to get the chest x-ray done, so if you have one that was taken recently, you can provide that and save a lot of time.