Thanks for the reply and suggesting the Cateye Volt 50.
My problem is that the Topeak saddle bag is one of those wedge bags that clips onto a bracket fitted to the seat rails. I am not sure if there will be enough room for another bracket although there is space for a light between the saddle and the bag. I will have to have a good look at the lights in my LBS to see if I can find anything suitable. I would prefer to mount the light above the bag as it will not be at all obstructed there. The bag does have a loop on the back for a light but it would be angled downwards if I used this method.
You'll never get 2 rail mounted items on the one saddle, they both extend in the same directions and would impede one another's click on/off set up.
Cateye do a universal fit seat tube clip for the 50 of their ridged band and knurled nut type, available in
Evans etc for a couple of quid. I find the Volt sits happily on this clip immediately under a wedge pack, when set up, the power button is on the underside so the clip and body of the light will butt very snugly up to the bag.
Amy of the cigar tube lights or the flat wide, usually 5 LEDs in a line, type would fit in a similar up close manner as long as the power button is bottom/back of the unit.
IMO though & especially for the relative bargain price, the Volt50 is a very very good light.