Windsor will be joined by 60 scouts at a dressed trestle table enjoying a Big Jubilee Lunch.
The event aims to encourage as many people in the UK to have lunch with their neighbours, friends and family on Sunday 3rd June 2012. It is part of the celebrations for The Queens Diamond Jubilee.
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The mayor claimed last week the bridge would cost more to cancel than to build. He said £37.7m of public money had already been spent.
The houseboat in Chelsea, west London, comes complete with three bedrooms, three bathrooms, a reception room and its own patio.
The city is one of a small number which has seen an increase in traces of the Class A substance over recent years.