If your contract says that your holiday pay runs from January to December and you neglected to take it all before the end of the year, you have lost it. Had you had a holiday booked before you left and they had agreed to carry it over into 2015, you would be entitled to be paid but since you had not booked it you would have lost it anyway as of the end of the year.

If your contract required you to take the holiday during the year to which it applied, then you have lost it. That would be perfectly legal. Your exact position depends on the terms of your employment contract - so you need to read that. I can't tell you what your legal position is, because I don't have a copy of your contract.

Citizens Advice Bureau

You need to talk to The Pay and Rights helpline.

Give it a google.

UK