Hot weather is very unusual in England but when is there you have to deal with.
Assuming that you are a trained fit rider with few month of competition under your belt, you should not need much endurance training. I would concentrate on speed work and power training and appropriate supplement and diet to help your fluid loss. Ideally training during the fresh hours of the day…..
Power training with short boost above your threshold for from a short 45 sec to max 5 minutes (no more than 12) , ideally using climbs and various of them during your training with complete rest between them.
Speed work few option:
a) Very short sprints on flat again complete recharge between them no more than 10
b) Motor pacing no more than 50k
c) Criterium racing
Diet and supplement try to eat more fruits and fresh salads than usual, plenty of carbs and less fats again for fast fuel, mineral salts are very popular and easy to buy, but try not to exceed as is always better for our body to source naturally from food.