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Thank you for all your replies.
Alavahalf, My husband did what you said he couldn't see any blockages, but after putting it back together again the cistern is filling up much much quicker. It still makes a little hissing noise though, it looks like the problem could be the rubber inlet washer it looks ok but thats were the hissing noise seems to be coming from, so we are going to replace it B&q do our particular make but its out of stock so had to order one from Ebay, should be here tomorrow.
Thanks again