Many auditoriums and other large venues now have a wire under the periphery of the floor that beams amplified sound directly to hearing aids containing a "T coil". I trust that this exists in the UK as it does in the US. This makes the sound much clearer.

Also, as mentioned above, hearing aids often have a "noisy background" setting. If yours do not have such a setting, ask your provider to add it to your hearing aid - they are not perfect, but better than nothing.