mike coughed up some electrons that declared:

Thanks for all the replies.

The problem relates to the ongoing saga of my mother's woes with
Anglian Windows which I've posted about here before.

Yes - I do remember now.

Anglian - another "tosser point" to them.

They removed a window, didn't prop it, didn't install a lintel, and a
triangle of bricks came away. The BCO came out and said a strong wind
or hard frost could bring the lot down.

snip

I've juts phoned my local BCO and he said that 12 feet is "hellishly
wide" and that he can say without seeing it that it won't be
adequate. He also said that it should have been done with a prior
building notice and that re-doing it should be done after submitting a
building notice.

Right - why not asked him if the LABC are prepared to prosecute or serve
enforcement against Anglian and/or their contractor. This is after all, the
whole point of Building Regs. How long ago was this done (original install
and the angle iron bodge)?

Maybe Hugo or one of the other (ex) BCO's here might be prepared to comment
on whether this is something LABC's would get involved with?

As far as what should go in there, Dave Plowman was bang on: BCO said
get in a structural engineer to do the proper calcs.

Tim, thanks for that link to Catnic. On page 41 they do have the sort
of U-shaped lintels I was thinking of -- although on the same page
they also have something that looks like angle iron, presumably a
beefed up version though. I might give their tech help a call
tomorrow.