The switch on my power supply (which looks identical to Andy's) has a 25mm square cutout, rather than the 22x30mm one used as standard these days so the Maplin one may not fit as it is 22x30mm cutout.
Probably easiest to just bypass the switch. You may be able to avoid soldering anything as long as the leads are long enough.
We first want to take the wire between the fuse holder and the switch and reconnect it between the fuse holder and the terminal block.
- Assuming that it looks like it will reach, cut the black wire that goes between the fuse holder and the switch as close as possible to the switch, leaving it connected to the fuse holder.
- Remove the black wire from the terminal block, cut it off at the switch end and throw away.
- Strip off 5mm from the loose end of the black wire and connect it in the terminal block from where you just took the other wire out.
- You should now have black wires going: Terminal block -> fuse holder -> Transformer. There should be no other black wires now.
We now want to remove the blue wire between the transformer and the switch and connect it between the transformer and the terminal block.
- Cut this blue wire off as close as possible to the switch, leaving it connected to the transformer.
- Remove the blue wire from the terminal block, cut it off at the switch end and throw away.
- Strip 5mm off the end of the blue wire now hanging free from the transformer and connect it to the terminal block in the place of the one you just removed.
- You should now have a blue wire going directly from the terminal block to the transformer with no other blue wires.
Make sure the connections you just made are good (tug on the wires in the terminal block).
Job done. Remember to switch off at the mains in future: a transformer draws current even when nothing is plugged in to it.
If at any time when cutting a wire you hear a ticking noise, run like the wind...
Have fun, Bob.