I already own a cordless impact driver, but I'm damned if I can find it! It's only a Parkside Aldi one, but it did a reasonable job until I left it too long and the Li battery got too low & wouldn't take a charge any more. A while later, I stripped the battery pack & rebuilt it with bigger cells, only to realise that I can't find the driver itself. It should be in the garage, but it's better at hide & seek that Saddam turned out to be...
After one last search yesterday, I picked up this today:

Toolstation has them on special just now at £80 under list - still just about £160, but it chucks out 200+NM of torque. Off to the garage to try it out...