Employment confusion and suspicion

We have a new client for a 'simple' tax return.

This client had employment until end Feb 2011. Unfortunately, his employer sacked him but has not provided a P45, or any payslips. He was employed by the same company for over 12 months, and net pay went direct to his bank.

The only proof of employment that I have are his bank statements showing the monthly pay received, his previous years P60, and the letter of dismissal from the MD of the company which says he is not entitled to pay in lieu of notice, but is entitled to unused entitlement to holiday pay, and this will be calculated, and forwarded with his P45, which never arrived!. 

Now the mystery ... the company 'employing' him only registered with Companies House in November 2011. There is a company with a similar name (and the same MD!!!!) which is in liquidation, due to a winding up order which commenced in 2008. The last accounts filed were for 2005!!!!

I contacted HMRC to get PAYE details and there is no employment recorded at HMRC for tax year 2010/11.

So what next? I have his total net pay (taken from bank statements) and the PAYE reference taken from the previous years P60. I can enter estimated employment income/tax, and provide plenty of info in the white space, and attach a scanned copy of the letter of dismissal, but what warnings should I give my client? Is it possible that HMRC will pursue him for any tax that hasn't been paid over, or will they pursue one, or both, of the 'employers'?

We do need to complete this return as he has 1 months self employment income, and two small pensions in addition to the employment income.