If you do any cleaning other than external cleaning at all, they are obliged by law to retain 20% (ex VAT) and pay this to the HMRC at the end of the month in which they retained it. The only way to avoid this is to get an exemption certificate from the HMRC
This is then kept safe for you by the government (aren't they kind) until you can prove to them at the end of the year that they owe it to you. You get no interest on it and you must present the certificate issued to you by the company who retained it.
If you are out by a penny to what they have on their records that has been retaind on your behalf, they can refuse to pay it to you until the amount you ask for tallies with the amount they say it should be.
They are a pain in the butt, and should be taken to task on the bureaucracy of the system, but we have to comply.
