Some let's look at this job for a guest room cleaner in West Kensington: http://www.gumtree.com/p/housekeepi...ian-or-russian-or-polish-speaking-/1103780205
You're quite right that speaking English is a requirement of the job, but so is the ability to speak Russian, Lithuanian or Polish. Why? What possible reason do you need a cleaner who can speak one of these languages in the UK? I suggest that the advert might as well say "Cleaner required - Russian, Lithuanian or Polish nationals only" because any UK national who is fluent in one of those languages probably isn't going to be working as a cleaner.
Possibly because they have a lot of customers who speak those languages?