Ok, these may be common in the UK, but I doubt that even.  These are 2 very nice examples of Avon 2 hose assemblies.  You can see from the picture they were made with no regard for expense.  The mouthpiece weighs quite a bit compared to even a heavy Hope Paige.  The construction rivals that of even modern rebreather mouthpiece in my opinion.  The hoses are one inch and one set is in better shape than the other but both sets of hoses are useable in my opinion.  You will note that there is a slight variation in the mouthpieces and are likely from different moulds or runs.

Price $250.00 each set.  Shipping on one set $7.00