I worked for a very upper-class restauranta few years ago. I had actually been there just under 3 years when I left.
After handing in my notice I was told they would be paying me less because holiday was calculated from April-April. When I started I was told it was January-January.
I didn't contest it and instead went straight to ACAS (UK Labour board basically). This restaurant also always paid £100 p/mo in tips regardless of how much they had actually taken. ACAS gave me a template idea for a strongly worded letter and told me to mention I had contacted them.
Surprise surprise, I was paid the almost £400 they owed me almost immediately. I didn't tell ACAS about the tips issue although looking back I really wish I did.
They had the nerve to tell me I should have spoken to them before trying something like that… Haha no thanks.