Many firms whose staff deliver public services have rules about accepting gifts from their punters, although back in the 60's and 70's there were stories of people being harassed by binmen if they didn't give them a tip at Christmas (as immortalised in Lonnie Donegan's My Old Man's a Dustman). When my mum came to England in the late 40's, the postman used to deliver on Christmas day and it was traditional to offer him a snifter rather than money.