Radial circuits offer a better form of power distribution, and heaters are far better off on dedicated radial circuits.  With rings, dependant on resistance due to increased load, only around 2/3 of the total circuit rating is available on each leg.  Whilst this offers a satisfactory form of distribution for ring mains with generally low-current appliances being plugged in, it is not ideal for high-load heaters.
You need to work out the total load of all your heaters, and other commonly-used appliances (fridge/freezer) on the circuit, and see whether this could come near or exceed the circuit protective device (fuse/MCB) rating -> I=P/V.  If it does, they need an extra dedicated circuit, or your existing circuit needs splitting into two.