Diagram below as promised. The left diagram is what you have now and the right shows how I would remove the Towerstat and connect the Heat link to the existing wires. Take care not to mix the two black wires up when moving them.
It appears from your photo that the Towerstat is fixed to a surface mounted pattress box. If so, this can become a junction box to contain the new wiring terminals. You can buy a blanking plate to cover it.
I have adjusted what I said earlier slightly, in that instead of running 4 wires to the Heat link you will see that I've only used 3 and added a link between the Heat link terminals L and 2. Electrically the circuit is exactly the same as before, but doing it this way has two advantages:
1) It will allow you to use standard 4 core cable (3 core + earth) to connect to the Heat link
2) You won't have to try and cram 4 wires into one of the new terminals
Earth wires aren't shown for clarity, but I can see an earth terminal in your photo. That can stay as it is. The earth wire in the new cable can be used to connect it to the Heat link earth terminal.
The wiring to the Nest Thermostat isn't shown, in case you plan to use a separate plug in power supply for it. If you do want to hardwire it, two new wires would connect T1 & T2 at the thermostat to T1 & T2 at the Heat link respectively.
Final note: I don't know what type of wireless thermostat is presently being used in conjunction with your RF receiver. If it is just a basic thermostat controlling only the temperature, and there is a separate on/off timeswitch somewhere else controlling the heating, that would need to be set to be permanently 'on' to keep the Heat link permanently powered and to stop it interfering with the operation of the Nest.
It appears from your photo that the Towerstat is fixed to a surface mounted pattress box. If so, this can become a junction box to contain the new wiring terminals. You can buy a blanking plate to cover it.
I have adjusted what I said earlier slightly, in that instead of running 4 wires to the Heat link you will see that I've only used 3 and added a link between the Heat link terminals L and 2. Electrically the circuit is exactly the same as before, but doing it this way has two advantages:
1) It will allow you to use standard 4 core cable (3 core + earth) to connect to the Heat link
2) You won't have to try and cram 4 wires into one of the new terminals
Earth wires aren't shown for clarity, but I can see an earth terminal in your photo. That can stay as it is. The earth wire in the new cable can be used to connect it to the Heat link earth terminal.
The wiring to the Nest Thermostat isn't shown, in case you plan to use a separate plug in power supply for it. If you do want to hardwire it, two new wires would connect T1 & T2 at the thermostat to T1 & T2 at the Heat link respectively.
Final note: I don't know what type of wireless thermostat is presently being used in conjunction with your RF receiver. If it is just a basic thermostat controlling only the temperature, and there is a separate on/off timeswitch somewhere else controlling the heating, that would need to be set to be permanently 'on' to keep the Heat link permanently powered and to stop it interfering with the operation of the Nest.