Life is tenacious....

Given the right conditions, life will flourish in the most surprising places. In full sun in the cement joining some bricks in a wall on Wilbraham Road in Chorlton, Manchester there was this plant. I've no idea what it is. Is it a British native or did it escape from someone's suburban rock garden? If anyone can identify it I would appreciate it. Not only was it growing but it appeared to be flourishing producing a mini garden in the most hostile conditions....