http://www.agsformule1.com/en/driving-course/program.phpThis is without doubt the best available. I know the AGS cars where never the fastest, but, I am pretty sure all these type of cars will be detuned anyway you will have a pretty good time.
BUT, this place also has an ex 905 V10 Peugeot on its books.
It won't be cheap, and to drive the top cars you will need to have driven a single seater before, but there are programs for all levels.
A bit cheaper you can try these people
http://www.racing-school.co.uk/based at aintree & rockingham you can drive a Forti F1 there.
OR
moving up in price again there is....
http://www.ascari.net/secciones.php?idioma=2&&seccion=15