The Taxes and Management Act is very clear as to what is a legitimate assessment to reclaim payments made taxpayers. It is a formal letter confirming the amount due, rights of appeal and debt management options should they be required.
An assessment is not simply a self assessment statement with an attached request to pay.
At LTAG we have found that in many instances taxpayers have been asked to pay without the proper assessment being served. Had the proper assessment been served then for certain taxpayer circumstances it may be that HMRC are out of time.