I second this. It is basically the best flight aggregator if you do not have a fixed date. The downside is it does not aggregate some low-cost airlines (like AirAsia) but no worry between the KUL-LHR route.
As far as I know, for this route, only MAS and BA (British Airways) offer direct flights and cheapest fare seems to be about 2.1k. If TS does not mind Vietnam Airlines (they are flying with Boeing 787 BTW,  ), you can actually fly with only 1.1k one way.
Most people who make a transfer will stopover at Middle East cities via Emirates, Etihad or Qatar Airway.

As for the train from London to Nottingham, you can look it up in the National Rail (UK's KTM) website . http://www.nationalrail.co.uk/