Got a mixture of 3/8" UK spec and 5/8" American style stuff there friend. You need a 608605 Adaptor from Parweld to fit the y-piece to the reg, then cut that 5/8" fitting off the hose and get some 3/8" nuts and 1/4" tails to fit your hoses to the y-piece.
any recommendations Richard? to be fair - its not the best regulator. One day it will be bang on 6lpm all the day, and the next day at 10lpm without adjusting the regulator at all....
What's your budget mate.
Gas arc, (victor esab), Harris, are decent brands to go with
My personal favourite are the offerings from elga but they are a small fortune.
You defo need a new one if your flow is irregular. Your welding will only ever be as good as the quality shield you provide for it.