it's a bit of an oddball suggestion - but there is a National Trust place at Osterley Park which has a tearoom - and it seems to be a requirement that all National Trust tearooms serves scones with jam and cream - might not be the full on cream tea, but might be better than nothing.

http://www.nationaltrust.org.uk/main...-osterleypark/

Getting there could be an issue without a car - it's down the A4 into London, but there is a tube station not too far away.