Hi there,
The rules have probably changed, but it used to be that you could take your test in your own vehicle if you so chose to. I know a few friends of mine did that. I'd be surprised if they have actually made the change from that though.
so theoretically, yes you can take your test in a LHD vehicle here. As pointed out, it'd be X % harder as you'd have to get used to the differences with driving LHD in a RHD convention country/road system.
Overall, I'd say learn and pass your test in a RHD, get used to the road system becuase you 'actually learn to drive AFTER you pass your test!' - depending on how good you are and the resulting confidence, I'd say then look at the possibility of getting the car you want in LHD if you really want. As I've mentioned before, this 'usually' means getting or importing an 'interesting' USA car. Don't be too tempted to bring over a 'normal' bread and butter car from the US, the amount of import duty, tax and shipping etc would most likely make it subtantially more expensive than getting the RHD version of the same car here.
Contrary to popular belief and a response on this thread, driving LHD here in the UK isn't as 'dangerous' as initially it appears. The F150 I have has the advantage of being quite big and so I get an SUV type view and that cancels out 95% of the visibility issues that most people think would be the case. In a LHD sports car, that visibility will drop substantially, however, when you drive such cars, you drive '2+ or as far ahead' as possible, which in turn, reduces the percieved risk.
Good luck with your driving and test !
Cheers! DtM! West London & Slough UK!