I borrow one of those 18v Makita HD battery grinders from time to time and with the right cutting disc, they go through hardened steel like butter. Seriously, I was shocked - I reckon you'd go through an Almax in 2-3 minutes tops, both links. You'd maybe need two batteries as they run down quick. As you mention, that's nothing in a busy London street.
I've got one of these at work, goes through most d locks with ease (releasing customers bicycles when they lose their keys), not tried it on a heavy duty model, would hope it would chew up the blade and drain the battery.
I borrow one of those 18v Makita HD battery grinders from time to time and with the right cutting disc, they go through hardened steel like butter. Seriously, I was shocked - I reckon you'd go through an Almax in 2-3 minutes tops, both links. You'd maybe need two batteries as they run down quick. As you mention, that's nothing in a busy London street.