I recommend the HI Kensington-Forum (see pictures below or
read a report here. The HI Kensington-Forum is my favourite considering price-performance). The price is often around 60GBP, so you will have to book two rooms (
www.6c.com ). The next tube station is less than 5min away.
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Pictures from hotel stays
Basic Hotel stays/nights/points calculator
Short overview: KLM FD, LH M&M