Thruxton
 

I was at thruxton on Sunday for the super bikes with regards to the runway notice quite long I know light aircraft and helicopters use field but could a small biz jet land there I know boscombe down is up the road

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The runway at Thruxton is 770 metres which is just 5 metres shorter than the one at Denham.
A Cessna 510 Mustang has visited Denham in the past.

And at least one Citation 500 has visited Thruxton.

Yes, physically some business jets could land there safely with no problem.
But they have a few operating restrictions:

VFR only
Not larger than 5.7 Tonnes MTOW for commercial operations.
Not greater than 12m wing span on the apron without permission.

I'd disagree with that wholeheartedly. A small number of business jets could land there with much reduced margins, and certainly never for commercial purposes. Likewise, takeoff would be possible but without any options should an engine fail anywhere near Vef. Although I'm rated on one such jet, I wouldn't even think of putting it into Thruxton. If you needed to use Thruxton, a Raisbeck King Air would be the machine of choice, and even then, it would be dicey.

Perhaps the OP had observed the length of tarmac as opposed to the runway declared distance(s) what with disused portion(s), displaced threshold and all!

He certainly hasn't looked at the state of that extra tarmac though...