I don't know if anyone is planning to go and watch this. If so, note that this year they are avoiding Thornton Heath and Croydon and going via Sutton (-ish) . More precisely their website says Hyde Park to Kennington via Westminster Bridge as usual, then:
Kennington A 23
Stockwell A3
Clapham Common A24
Colliers Wood A24
Rose Hill A297-A217
Banstead A217
Burgh Heath A217
Reigate A217-A25
then back to normal
A23 through Earlswood, Salford and Horley and A2219 to Crawley (half way)
and on to Brighton