I have recently being trialing Mountain Fuel Sports Nutrition on and off the bike and really happy with the products, therefore I will be using them for training and the Lejog 2021 record attempt.
They have a great range in products from gels to bars, taste great and easy on the stomach, gluten free and vegan.
https://www.mountainfuel.co.uk/
Mountain Fuel is run by a small team of individuals, with a passion for nutrition, physical activity and the outdoors, Rupert Bonington is the MD, you may have heard of his father Chris Bonington the "Mountaineer."
I am not sponsored by them but they have kindly offered our members a 15% discount and free delivery on all products, just add StirlingBC as a discount code on checkout.
All the info is on the website, but happy to give further recommendations here.......