I have to say Wembley, in its later years wasn’t the greatest track for racing !
To be fair with the modern style of speedway , the Manchester raceway is the best track for racing that has been used in the UK. As a “stadium” honestly Wembley has to be the best - with its huge capacity and atmosphere, and ability to handle the huge crowds.
manchester is only half a stadium and has little atmosphere in comparison with industrial units surrounding half the site, and poor crowd capacity leading to high ticket prices.
Glasgow is mooted - good track but again poor crowd capacity leading- high ticket prices .
with a 6 team premier league lucky to have 2 GPs in the UK tbh.