I have somehow ended up with a spare 12v Li-ion battery, so I took a punt on some "Type R" car strobe lights from China of
EBay which actually arrived today.
I just did a quick test and they are great flashers, two strobe bulbs one flashes three times then the other and so on, the flash speed can also be varied. Although I will need to swap the blue covers for the white ones before I use them for real as the blue covers make them look just like Police lights. They do come with other colours, red, green, orange and pink.
Combined with all the forward facing lights I have already, if I actually turned them all on I would look like something out of Close Encounters of the Third Kind, just a little slower and closer to the ground.