Light switch won't turn off after fitting a new light bulb

Question

Thought installing a cheap "smart" light bulb would be a harmless operation. Here's what I did:

1. With the light switch off, removed the old light bulb
2. Installed a new light bulb and flick the switch on
3. The fuse box switched off all our lights, so I unscrewed the new bulb and put the fuse box switch back on

Now, the light switch on the wall won't turn off (like it won't "click" into the off position).

Here's the old working bulb:

Here's the new candle "smart wifi" bulb (I used their supplied B22 Bayonet Adapter) which caused this issue:

Can anyone explain what has gone wrong? I'm also intrigued into the (protection?) mechanism of the light switch which means it cannot be turned off anymore. More importantly, how do I fix it? I'm in the UK.

Bulb specs: They both say 220-240v on them. New bulb which caused this issue is 5W, the old working bulb is 15W.

Answer 1

Since you mentioned the switch would make an audible "click" sound before the replacement and afterwards it doesn't, you should investigate the switch further.

This is easy when you use some sort of instrument that tests continuity. Use a Digital meter set to Ohm's or assemble one by wiring a battery in series with a flashlight bulb.

By connecting a lead to the switch terminals both instruments will show if there is a continuous flow of electricity through the switch. If they don't the switch is bad.