LO,
I recall seeing a figure of 15% quoted as the UK content in the F35, but I'm damned if I can remember where so I cannot link to the source. However, it does seem to stack up with your arithmetic.
Meantime, Mr Hammond has been talking to
The Telegraph according to
Defence Management. I'm not sure if this is an official announcement or government by media but, for what it's worth, it looks like hovering may be back in fashion.
F-35 'facts have changed' since SDSR - Defence Management