If you're planning to run a company from abroad, you should first contact the possible agents and ask whether they can store annual accounts for you which you will have to prepare at least every six months and store at your registered office address. I didn't realise that and now have to change the office address.
I've recently contacted Capital Business Links LTD, and am really impressed with their attitude. They're not official Companies House agent, but they can also register a company for you and provide you with a registered office address. http://www.cblfinance.com/
They charge 90 quid a year, so a bit more than for example the Companies Made Simple, but they forward any kind of post to your e-mail address. They always forward statutory post and a reasonable amount of other mail. At least you might be sure that none of your letters will end up in a bin.