I think a problem may lie in the Select statement, but not sure.
$productsql = "SELECT cid,filename,txshort,pence,txlong,image FROM products,categories WHERE products.cid = categories.cid AND categories.dirname = $file";
$productResults = mysql_query ($productsql);
$productRow = mysql_fetch_array ($productResults);
$ProductName = $productRow["filename"];
$ProductName1 = $productRow["txshort"];
$sum=$productRow["pence"]/100;
$sum1= $sum/100;
$sum2 = $sum1*17.5 + $sum;
$sum3= round ($sum2,2);
$ProductName2 = $sum3;
$ProductName3 = $productRow["txlong"];
$ProductName4 = $productRow["image"];
echo "<br><img src= http://www.page.co.uk/image/$ProductName4></br><br><strong>Product Code:</strong> $ProductName</br> <br><strong>Item:</strong> $ProductName1</br> <br><strong>Price:</strong> £$sum plus VAT (£$ProductName2 inc)</br> <br><strong>Description:</strong> $ProductName3</br>";