I'm quite intrigued if those people cannot use cars with the steering wheel on the left in UK because of the law or they just have not used to do this with the steering wheel on the other side of the car. The question is also applied for the UK guys driving to EU: can they use their British cars in EU?
Here in Russia we have a good bunch of used cars from Japan with the steering wheel on the right. Well you'll hardly spot one in Moscow or Petersburg but moving to the East over the Ural mountains its number is about 50 percent (Novosibirsk including) and rise to 90 persent for "Far East" like Vladivostok.