Thank you to all of you who have responded/contributed to this thread. The complete units is available on eBay for around £12.00, so Tonyr1084 's comments on replacing is quite valid. However, I am also trying to use this as a basis for learning/experimenting with electronics, as the circuit does not seem to be too complex - Thanks LesJone's for the sketch.

I will be looking at all the comments and suggestions over the weekend and will feed back accordingly. And Tonyr1084, thank you for your concerns regarding safety. I use a 'trip switch' socket when testing, and always close the device before plugging in - so whilst I appreciate the advice given by
KeepItSimpleStupid,, I am not sure I am brave enough or competent enough to attempt the tests he suggests

Here's looking forward to reporting some positive results soon

 

I don't know Dick. This is how mine work. That's all I know about it. If you unplug it the light goes on. If the power goes out the light goes on. When power is restored the light goes off and the battery(s) charge(es). If you take the light out of the cradle it goes on. You can push the button and change the function from dim to bright, side light or strobe. Or you can turn it off. Stand it in the base and again it's ready to come on when the power goes out or you pick it up out of the cradle.

 

Can you, at least pull off measuring the DC voltage across the 4.7 uF capacitor with a unit not charging (Torch not on the base). A semi-broken one should be fine too.

You can solder two wires to the appropriate points and bring them out and taped down away from each other.
Paper, cardboard - just not metal.

Your mains voltage and frequency. UK is 230 Vac and 50 Hz, so i assume that's right. You really need to get a suppressor installed either across the mains or across the 4.7 uF cap. I can find a suitable component from Rs-online. It has to work without them first,

 

I had a similar fault on one of these chargers. The 2K4 resistor and .22UF C had failed along with the 13001 transistor. I replaced the defective components but found that the 13001 had failed again. I then discovered that the pin outs for the new 13001 were the mirror image of the original transistor. The centre pin is the collector on both but the base and emitter are swapped over on the new ones. I installed another new 13001 the correct way round and everything is now working fine!

 

@mvlb Welcome to AAC.

It's possible one manufacturer may have designed their transistor a little different from normal practices. However, it's also possible the manufacturer may have inadvertently swapped them then discovered the error. Those bad parts may have been sold to a clearing house from where you may have bought yours. In other words, factory rejects get sold all the time on places like Amazon and others.

But as long as yours worked out - great.

Again, welcome.