If you can throw a reasonable chunk of time at study each week the 7 exams can be knocked out in about 3 to 4 months with relative comfort. The exams are held every 2 months for the IR, and only at Gatwick.
You can train in your aircraft providing all the paperwork is in order, and obviously providing it's airways legal. It's fairly easy to get the aircraft approved for test. Here's the standards document for test approval:
http://www.caa.co.uk/docs/33/srg_fcl_07_A.pdf