Another recommendation for MandS here. They were really quick when my wife's bike was stolen from her work. It probably helped that she tends to keep receipts for everything and sent them a very detailed list of all the parts. After about a week we had an offer from them that was more than we were expecting and they were quite happy to just send a cheque.
One thing to be careful of is that when it comes to renew they wont necessarily send you the cheapest price. Go back on to their website and get a quote that way, as it's often cheaper. That's true of a lot of insurance companies these days, just saved over £100 on my car insurance doing this with Aviva.