I arrived promptly at Mrs S's ready to replace a lightbulb in her bathroom - she kindly showed me into the bathroom and pointed up (in the darkness) at the ceiling fitting. Not for the first time I said a silent prayer to the designer who thought having a torch in a phone would be a good idea...

After unscrewing the shade, it was an easy task to remove the existing bulb, but I then discovered the new bulb wouldn't fit - unfortunately the replacement bulb was the wrong model with only two pins, whereas the bulb being replaced had four, and in different locations on the central fitting, so there was no way the replacement bulb could be installed.

I explained to Mrs S the situation and told her I'd report back to mission control that the referrer would need to exchange the new bulb provided with the correct model. Once Mrs S has the correct bulb, it should be a reasonably straightforward task to then fit it into the socket, and hopefully Mrs S will then be able to bathe in the light once again.