Drive,
You friend is wrong, HM Customs will not let you get away with this unless, you can show that the 2 business's are entirely seperate, bit difficult to do if you are carrying out the work for both domestic and commercial client's.
You pays your money you takes your choice I am afraid, the upside is that a VAT registration could be a bonus with domestic, maybe because it shows that you are a bona fide business, maybe!
Regards,
Rob