Yes very interesting, but not actually true, though. 3000 defenders of Drogheda were massacred after the town refused to surrender. It was true that Cromwell lost control of his men, but the same thing happened whenever an army was forced to assault a fortified place after a 'practicable breach' was made (cf storming of Magdeburg 1631). This part of Cromwell's career can be related to the European Wars of Religion. A great many lies were told by both sides.

So few British actually enlisted in what was to be the British Battalion of the SS that it never formed. The SS did recruit from other European countries in much greater strength after these countries had been occupied details here
It certainly makes me wonder why someone would start a thread like this claiming a 'British SS unit' when the facts are that there were 20 British and 10 Commonwealth prisoners of war in this so-called unit, and they never say any action!