Any programmable thermostat with voltage free contacts will replace what you currently have. If you are happy with the thermostat location and it works well in its current location, go for a wired thermostat. I would normally go for Honeywell [CM907], Danfoss [TP5000Si], or Drayton [Digistat+]. As a general rule of thumb, and as with most products, you get what you pay for. Have a look at the specifications on line to make sure they have the facilities you require, and you might want to check the instructions. Some are more complicated than others to use.
If the thermostat would work better in another location, a wireless thermostat that can be located anywhere would also be fine. The receiver box would then go where the current thermostat wiring is located. The previously mentioned manufacturers offer 'Wireless RF' versions. Nest and Hive offer remote control from a smart phone as well as other facilities via WiFi, but cost considerably more.
If you find a thermostat that you like, feel free to post back for a suitability check.
I can't see all of the wires and exactly where they are connected, especially where they cross over each other, but looking at the photos and the connections together, I believe that one of the incoming cables will have its wires connected to the thermostat terminals numbered 2 and 3. These will be the switching wires. The other cable will be the 230V mains supply, the red of which I believe will go to the Timeswitch 'L' and the black to the Thermostat 'N' If the reality is different post back what you have.
