As far as I am aware, use of the word "Maintain" in ATC instructions is not ICAO. Because of the possible confusion mentioned by eyeinthesky, ATC in the UK is being told not to use it at all.
411A, yes, often Brits do have a problem in the USA. It's not only over-simplistic but also insulting to say that "they don't seem to listen, let alone understand". What's more, comments like that do not aid the situation, nor assist in understanding a potentially very dangerous problem. US pilots often have difficulty in the UK in exactly the same way. Part of the problem is difference of accents, part is that US Aviation English has numerous (unfiled) differences from ICAO standard, part is that US ATC and pilots don't even stick to their own "standards".