Bypass a faulty timer unit on a stoves 720ef cooker. . . . My partner tried this today on my cooker and now there is no power to the cooker at all!! Is there a chance he's managed to do the wr

should be able to have on manual as for normal cooking

Try taking the power wire that goes into the timer and the power wire that comes out of the timer and put them together not hooked to the timer and that should work. If that works you should solder them together and electrical tape them good.
Make sure the power is off when you do this so you don't cook yourself.

I have a similar problem and contacted Stoves. Apparently the timer unit is now obsolete which means replacing the complete oven!

You obviously have a power loss somewhere. The oven will not work unless a time is set on the clock. I would suggest you have problem with the feed to the cooker which an electician should be able to check it out. If anything else is wrong on the cooker, it shouldn't reset the clock.

The handbook says:-
To cancel the automatic setting and return the oven to manual operation, press the cook time and ready time buttons simultaneously. These are the second and third buttons from the left. If you have done that and it is not working, try turning the complete oven off for awhile - say 30 mins and turning back on. If this still doesn't work then it may be that the timer/clock has gone faulty.

From the handbook:--
Press the MINUS button to listen to the first tone.
Release the MINUS button and press it again to listen to the second tone.
Releasing the MINUS button after the tone has sounded will automatically select that tone.

I have posted how to use the timer on the 720 on other solutions. Try that to see if it works.

When you say the main fan, do you mean the background cooling fan or do you mean the circulating fan in the bottom oven?
Do you have the handbook for this oven as the wiring diagrams are included in it. If you haven't, you can take a copy from my BT Digital Vault - all I need is an email address to register you.
Looking at the diagram, the power for the cooling fan comes via the timer board. If, as you say, the fan doesn't work at all, the timer board could have gone faulty.

Supply an email address and I will validate it on my BT Digital Vault to give you access to take a copy of the Handbook.

To take off the front button panel.
First power off the cooker, then remove the three right control knobs - they are just push on and push off. There are flats on the spindles matching contours on the knobs to ensure thay go back correctly.
Lower the top oven/grill front. Under the front button panel there are three screws going upwards. One at each end and one in the middle. Remembering how they are installed, remove them. The panel will now be loose but it is held in postion by two or three lugs which are along the top inside edge of the panel. They, from what I remember, hook into the inner panels of the cooker. I think you have to lift the lower edge of the panel towards you, to overcome the upward bend of the lugs.
The buttons for the clock are purely push fit and if you want they can be removed using a thin bladed knife.
I have to say that if you want complete access to the clock, I think you will have to take out the complete oven from the unit and take the top off, so be warned. Instructions of how the cooker is mounted are in the instruction manual.
Putting the front panel back I found to be fiddily - ensuring the lugs are located correctly, especially the one by the clock doesn't always want to work. In the end I left that one not positioned correctly, so in effect the front panel is slightly out at the left hand end.
Best of luck!