In order to claim back VAT, you have to first register.
Then you have to charge VAT on what ever work you do.
Then you pay that money to the VAT man.
If you get something wrong, they fine you.
If you are late making a payment, they fine you.
If you are late paying the fines, they fine you.
They charge interest on late payments.
They come and inspect your books whenever they want.
They can turn up at 7am, and it doesn't matter that you have work booked for that day, they can just take over your office or home, and go through all your paperwork.
If they want, they can take all your paperwork and your computers away to their office.
If they find that you have underpaid VAT at any time, you get fined and charged interest from whenever you should have paid, up untill you do pay.
You become an unpaid Tax collector who can be fined for any errors you make.