He should have given them a mnimum of one week's notice - possibly more, but let's try and hold the line at one week.
Here is the reason.
http://www.direct.gov...gorretiring/DG_175837
He is therefore in breach of his contract.
However failure to give the required notice does NOT entitle the employer to withhold the wages - to do so is an unlawful deduction of wages.
This is confirmed here
http://www.emplaw.co....tpage=data/098001.htm
So the position is that the employer can't take the law into his own hands and hold back money - he has to go to court and make a case for breach of contract and damages for that breach.
Construct a letter along the lines of 'You owe me the sum of xyz in wages that were due yesterday. Failure to pay by tomorrow will be construed as an unlawful deduction from wages and will result in e taking legal action to recover the money'.
It might do the trick.