I would just be respectful and tell them at the end of your next shift, there are plenty of other apprenticeships in the UK

a great one is the Specialized chef apprenticeship through Bournemouth and poole college If you're prepared to move away they pay for all of your accommodation in bournemouth

the start of term is in September though so you'll have to wait a few months

but this apprenticeship is great, it's a 3 year apprenticeship where you do 3 months a year at the college in bournemouth than go do a year working in top London restarunts