Thanks for your reply.
Yes, the heaters are on a separate circuit switched through a timer and a separate meter. Once a new meter is installed, there will be enough space to connect it’s timed output to the 2 way double pole isolator switch/ fusebox that feeds the two storage rads and hopefully, it will be possible to connect the deep element of the immersion heater to this supply, also, again via a similar isolator/fusebox to provide a supply to the hot water timer for 1-2 hours every night. We have an electrician to help with this. I was most worried that EON’s new meter may not be compatible with other suppliers to which we may want to switch in future.