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Thanks guys for your answers - i think maybe i should have made it £2, but I am not so flush that I can splash fivers about.
I tip in restaurants if the service is good - if they put 10% on, and the service is not up to standard, i will deduct it. they are not entitled to add it on, so they don;t argue.
joeluke and starbuckbone - I have referred to my wonderful wife as 'the present Mrs Hughes' for some time now - and it is intended ironically - we have been together for thirty-one years, and married for almost twenty-five, she is the first, last and only Mrs Hughes - it's just a bit of humour.
dee-sa - we were in South Kensington, which is now outside the Congestion Charge area.
Old-Geezer - my wife was on business, so the hotel was booked by her employers. They always use top hotels which put us in the position of being slightly unsure of the tipping criteria, hence the query.
Thanks again guys.