On cheques of over pounds 1,500, the society takes seven working days after the cheque is paid in, a period that can span two weekends.
In effect, the real clearing time can be as long as 11 days.
Dr Wyatt checked with a few other banks and building societies to find out the clearing time for their cheques.
He discovered that Halifax and Abbey National did not operate the same sort of rule - all cheques are cleared after three working days, whatever the amount.
'The cheques are usually paid in by my agent. A large number of them come in above that pounds 1,500 level,' Dr Wyatt said.
Nationwide said the length of cheque clearance time was set according to the degree of risk the society was willing to take on. A society spokesperson said: 'A cheque may not actually be cleared after seven days.'
Many cheques are processed through the postal system, which can add delays and increase the risk that someone can withdraw funds on the back of a cheque that subsequently bounces.
He said that the longer the clearance time the less the risk to the bank. Nationwide offers a service that will clear the cheques on the next working day.
It costs pounds 12 per cheque. Nationwide has written to Dr Wyatt to offer him this service, but this has only served to enrage him further. 'They can whizz any cheque though the clearing system if they want to. It just shows how tenuous their argument is.'
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