>>>he did threaten to sack me
He's
already sacked you! You had a contract, as an employee, to work at the pub. The new boss has terminated that contract. (i.e. he's sacked you). Whether you then do the same work as a self-employed contractor is irrelevant; you've still been sacked as an employee!
In the first instance, refer the boss to this web page:
http://www.hmrc.gov.uk/employment-status/index.htm
If that doesn't work, seek the advice and assistance of HMRC.
However . . .
>>>I get no extra pay for bank holidays or for Christmas, New Year . . .
Irrespective of whether you're an employee or self-employed, there's absolutely no reason why you should. (Public holidays have no special place in employment law). I've worked behind bars on Christmas Eve, Christmas Day, Boxing Day, New Year's Eve, New Year's Day, etc for the usual rate of pay. It's perfectly lawful.