It is sometimes not generally recognised that there is a whole family of starters for flourscent lights - not just one. These are rated for a range of tube wattages & sometimes for single or twin tube circuits.
Some suppliers only stock a 'universal' starter which will usually be OK for the common tubes eg 4 foot - 36W or 40W, 5 foot - 58W or 65W, 6 foot - 70W or 80W but often will not work at the extreme ends of the range, like your 15W.
The consequence of using the wrong starter is often that the tube will flicker/flash and fail to start properly...........
Thanks and no I did not know this.
The 15W tubes were sent by a specialist together with starters so I am sure the starters would have been OK.
I have looked at the electrician's one that did not work and it says it is a glow starter with condenser 4-85W so that should have been OK too. Apparently this one did not work because it was not put in properly and was wobbly.
All still working fine.
Thanks for help
JamesEB