On 01/06/2021 16:54, williamwright wrote:
On 01/06/2021 16:19, Jack Harry Teesdale wrote:

I have tested with my multimeter and get approx 240v at the
lampholder, so not a broken neutral.

I bet that 240V drops almost to zero when there's a load (such as a bulb).

That was my thought, perhaps a poor connection through corrosion.