My basic question is can the police in the UK accept refreshments from the public when they are at a crime scene?

Years back I gave tea and biscuits to police at a road block near my house, but that wasn't actually a crime scene.

In particular, can they accept if:

1. The person is a witness
2. The person is a possible suspect

or only if they are neither of the above.

And would it be limited to a cup of tea, or could someone say "hey we've cooked supper, there's plenty to spare, would you like a plate full?" and the police being able to say yes.