Reclaiming VAT is not a separate application. You claim it on the return, by putting the VAT you were charged on business purchases into box 4, and the difference between that and the VAT you charged is what you pay or get back. What decides whether a particular purchase belongs there is not the receipt total but three tests, and most disputes are about the third.
The three tests a purchase has to pass
First, the VAT must have been properly charged: a supply that was zero-rated or exempt carries no VAT to reclaim, however confidently an invoice shows some. Second, you must hold evidence, normally a valid VAT invoice showing the supplier's registration number, the date, what was supplied, the rate and the VAT. Third, the purchase must be for business use. Mixed use is apportioned rather than claimed whole, and the apportionment has to be defensible rather than convenient.
What cannot be reclaimed
Business entertainment of customers is blocked. So is VAT on a car bought for business use where there is any private use at all, which in practice is nearly always, though leasing and commercial vehicles are treated differently. Anything used for personal purposes is out to the extent of that use, and anything relating to exempt supplies you make is normally out too. Those exclusions are the reason a box 4 figure built from a bank statement is usually wrong and one built from invoices usually is not.
Purchases from before you registered
You can normally reclaim VAT on goods you still hold at registration that were bought in the four years before it, and on services received in the six months before it, provided they relate to the business you are now registered for. This is genuinely worth doing and routinely missed, because it requires digging out invoices from before the business was thinking about VAT. It goes into box 4 on your first return.
Questions people ask about how to claim vat back
How do I claim VAT back?
Through the VAT return: put the VAT you were charged on business purchases into box 4. If box 4 exceeds box 3, HMRC repays the difference rather than you paying it.
Can businesses claim back VAT on everything?
No. Business entertainment is blocked, cars with private use are normally blocked, personal use is excluded proportionately, and purchases relating to exempt supplies are usually not recoverable.
Can I reclaim VAT on things bought before registering?
Usually yes: goods still held that were bought in the four years before registration, and services received in the six months before it, if they relate to the registered business.