Gordon at Work and Safety has always been very helpful. I have bought two pairs of Muck Master Muck Boots from Work & Safety in the recent past, which sadly both leaked after a few months of wear.
Gordon suggested I try Dunlop Snug Boots as an alternative to Muck Boots. The website suggested to size up. I am a size 5 but have bought size 4 muck boots in the past. I ordered a size 5 Dunlop Snug Boot. They fit perfectly, they are cosy and I can already see why they were recommended as a better alternative. The toe and sole are moulded in what appears to be one piece. The muck boots had a seam and that always appeared to be the point of water ingress. It is still early days for the snug boots but at the moment I am delighted with them.