Most casters that shoot line, shoot only on the forward stroke.
I was taught to practice shooting some line on the back cast as well. If you work on shooting some line on the back cast just before the delivery cast, it will increase the distance. The extra line into the back cast just before the delivery increases the line mass and that will increase distance if you can handle that extra mass for the forward cast.
Just try it and see if it helps you. If you cannot handle the extra line on the back cast, this is evidence that your back cast needs work to equalize the power of the backcast vs the forward cast.
Logically, if you have a symmetrical forward cast and back cast strokes, and you can shoot line on the forward stroke; you should be able to shoot on the back cast as well.
I had an opportunity to have my casting stroke analyzed using the
Sage Casting Analyzer. It showed me that my stroke was asymmetric with a stronger forward cast than the back cast. My problem was both a weaker stop and less acceleration for the back cast. I also had some forward creep on the forward cast.
Most casters think that if they cannot cast far enough, they should work on their forward cast. Actually most casters have an asymmetric stroke and they need additional work on their back cast to cast further. It is counter intuitive but working on your back cast will lead to a stronger forward cast.
Here's a non conventional way to get extra distance. Get a step ladder. This will elevate you higher off the water and this extra height will allow you to cast a bit further. This is a strategy that still water fishers on Pyramid Lake in the USA use. I don't know if this would be legal in Great Britain but it is in the USA. If you do so and use a shorter ladder, attach a float connected to your ladder with a rope so that you can locate your ladder when you go to shore for a "bathroom break" or lunch.
Pyramid Lake