You're not the first to suffer this and I am certain you won't be the last.
Water and dirt get trapped in and around the spring pans (the part that's snapped) and cause it to rust away.
It's fairly common to peak under and see ream beams that are really scabby, I managed to catch my sister '04 before it got too bad, I ground it back, treated it with rust stop and waxoiled it, two years later and it still looks like new.
You really want a new one as with a used one, you could end up with something that's nearly as bad and may soon fail again. Like I wrote, it very common to see rusty ones.
You'll not weld it up either as you can't weld rust, by the time you get back to good steel, they'll be feck all left of it!
You'll no doubt need new shocks, they look about to rust through as well and to finish the job, new springs, as soon as the powder coating flakes they start to rust and MOT testers love to spot them.
Give Shop4parts a ring, I'm sure they'll be able to help you with everything.
Also there's a dealer that specializes in parts with some discounts, SG Petch.