Problem with bathroom towel rail. Bent tails.

Currently no kinks? Obtain a 15 mm internal bending spring, insert into pipe so that there is spring right past the bends. Then simply bend back and remove spring.

That last sentance is the Haynes Manual one. 100 mm doesn't give you much to apply force to the pipe with. You don't want to dent/kink the pipe by whacking it or you'll have fun getting the spring out. Levers and load spreader blocks are my thoughts ATM. The spring may still get trapped but if you twist it in the right direction it wind up and reduce in diameter.

Are they bent right against the floor, or could you cut them off and leave enough sticking up yo solder a end feed fitting on.

Also have you checked if you free the valve from the rad, whether there is any slack pipe that can be pulled up from the floor? (if under the floor it on a horizontal run, there ought to be some movement available).

The pipe will have to be free of any water as even the smallest amount may/will stop the solder from flowing. In similar circumstances I've used a wet and dry vacuum cleaner to suck out the remaining water. Albeit on 22mm, in true Blue Peter fashion I used a small length of mini garden hose pipe into the vacuum clear hose and used a 5p plastic carrier bag stuffed up the vacuum hose as the seal around the hose pipe.

Thank you Dave, good advice. Currently no kinks or splits. Somewhere or other I have a 15mm internal bending spring. Lord knows where, haven't used it in years. Will try to find it or perhaps get another. From memory, my experience of this was not good. I absolutely agree with what you say about whacking it. Perhaps a bit of hardwood bored to 15mm, bandsawed in half and then firmly clamped to the copper. This should allow some easier manipulation of the tube. Of course that would leave the lower end very vulnerable. Perhaps in combination with a bending spring this may work. Nick.

The left bend is fairly close to the floor, 1/2" or so above. Right is perhaps a smidge higher out of the floor. Not enough to attach a fitting without removing a bit of stone. This would not be easy. I have checked pipe slack and there is barely 1/4" lift on either side. IIRC, this pipe runs through, or under, one of the floor supports. I can't remember. Thanks again, Nick.

Indeed - I would avoid that problem by using copper push-fit fittings.

Decide exactly what shape the replacement pipe needs to be, start with more pipe than you need and use a wheel and lever type bending machine - not a spring - to bend it to that shape. Then cut the surplus off the ends, and re-assemble.

Remove the radiator valve and (using the valve nut and olive still in situ) attach a metre length of straight copper tube with a compression fitting. You can then use the extra metre as a lever using blocks of wood against the wall and your foot to brace the pipe as you attempt to straighten it. Perhaps heat to cherry red the position where the pipe needs to bend back while applying very gentle pressure at the top of the extra metre of pipe.

If you are going to hammer towards the top of the existing pipe still install a sacrificial compression fitting that you can discard afterwards.