A staggering 7.5 million Brits could be in for a cash windfall from the taxman, with HMRC's P800 forms indicating potential tax rebates.

Taxpayers across the UK are on the edge of their seats as nearly eight million could see a boost to their bank balances courtesy of HMRC's P800 tax calculation letters.

RIFT, the finance experts, have crunched the numbers and forecast that a whopping number of individuals might receive the coveted P800 letter this year, signalling they've paid too much tax and are due a refund.

Back in 2015, seven million PAYE workers were sent these forms, which affected around 26.5% of employees within that system.

With more people now paying through PAYE, the same percentage today would mean close to 7.6 million taxpayers are in line for good news.

Bradley Post, RIFT's managing director, shed light on why so many might be getting refunds, stating: "HMRC's PAYE system is an extraordinary machine of tax collection, but it isn't perfect and millions of mistakes are made every year. However, HMRC's internal check and balances system means that it often spots these mistakes in hindsight and does all it can to ensure people are either refunded, or top up what they owe."

The expert encouraged individuals to keep a close watch on their mail for the potential "very good news coming your way". He also pointed out that while HMRC can easily identify simpler cases, those with more complex tax situations might benefit from "appointing some tax refund experts to ensure that they receive every penny that is owed to them".

So, what should you do if you receive a P800 letter from HMRC?

This letter could indicate that you have either overpaid or underpaid tax, and the balance needs to be settled either by receiving a refund or paying the remaining amount to HMRC.

The letter will clarify which category you fall into and what your next steps should be based on your situation. If you are due a refund, RIFT experts recommend using the HMRC refund website app as this is the "fastest way" to claim your tax rebate.

Those who cannot use this option or fail to respond within 21 days of the form being issued will simply receive a cheque from HMRC in the post. Individuals who have underpaid their tax will be informed of the amount they owe and must pay this to HMRC as soon as possible.

If you believe there is an error with your final P800 calculation, you can challenge it by contacting HMRC.