Having a good agent and a good accountant is pretty important, especially if HM posts you to a place where it's not easy to take care of stuff like tax returns.
I had property let for about 15 years when I was working overseas, and reckon that the accountant covered her fees by what she saved us in tax. Perfect tax returns also will ensure that you are the "grey man", and HMRC will be less likely to take a deeper interest in your business.