Firstly, Have you got a contract of employment? If you have, then have a good read about your holiday entitlement. If it states that you are entitled to a set number of days per year and you had used them up prior to your two weeks off over Christmas, then he is probably not obliged to pay you. It also depends on when your holiday year starts; if it is in April and you have for example 25 days holiday entitlement a year, then that entitlement will accrue as the year wears on, you couldn't just take 25 days paid holiday at the start of the year. However, if the holiday year starts on Jan 1st, then you will have started accruing your allowance from this date and so far would only be entitled to a couple of days paid holiday. There can be variations stipulated in an individual's contract, but this is pretty standard.
If you don't have a contract of employment, then I'm not sure what to suggest. There will be minimum rights set out in the law, but it probably worth calling the Citizen's advice, they are brilliant at offering advice around these sorts of issues and it's free!
(I'm not a lawyer or solicitor, but have had employment law training in my role in recruitment and HR).
a bit light on retro rides right now!
05 Cinelli estrada
93 Saracen Ltd Edition - In need of love
93 Ozone O2 E-stay (the wife's)
2013 Whyte 129-S