Update:
So this is what I bought. The first suggestion!
https://www.NoLinkingToThis/p/dewalt-dce088d1g-green-self-levelling-cross-line-laser/5930k
I thought it through. I don't want disposable batteries and I did want to use it outside so a rechargable green line laser it was. I didn't want Chinese either so there you go!
Made a wasted trip in the snow to my local Lidl to try and find a £20 quid parkside laser. Looking online I'm not sure you can buy them anymore or if they are being made at all. Still think they have to be worth the money though.
The DeWalt works fine. I'm still getting to grips with it. Outside it marked a beautifully straight line for some conduit that I ran.
Inside for the downlights it was also useful. For instance in the kitchen I was able to run a series of spots perfectly in line with worktop.
What I haven't gotten to grips with is painting a perfect right angle on the ceiling. I have a gimble
with spirit level on my tripod. That's fine for most work. However I need to turn the gimble 90degrees upwards to get the cross on the ceiling. I can't seem to judge it by eye and the laser just keeps flashing to tell me it's not possible to self level. Maybe I need a different gimble, or maybe I just need to read the instructions?
Anyway it's a very robust but of kit and it's definitely handy. Just wondering if any other DeWalt tools will fit the small battery?
Cheers.
Spynage