There's a place near my house does car bits & pieces, engines & the like. Sign on the door says they weld aluminium, but they've probably never done work on a bike. I remember asking if they could weld lugs to a CRMO frame, they pointed me to a guy with a MIG setup in a nearby garage. We did chat briefly about aluminium welding, but I can't really remember coming out of there thinking I should scour eBay for cracked Rippers.
I'm in Plaistow, fairly near to Barking. Place is called Durlings.