I have found that "seam tape" Sue, thank you for your advice. It has been recommended by others too so i'm gonna go for it....
To buy that tape is gonna cost me no more £25 while to buy a whole new liner for the size I need is gonna cost me £276!!!!!
Already I have to give away the old (OLD!!!!! are not even 4 months) pump,filter and UV almost for nothing, at least I can keep the liner. I know is a chance I take trying to glue the old and new liner together but is worth taking it.
276-25 = £251. I add another £140 and I can buy a new pump, UV, vortex and filter for the new pond.
Once again thanks for the advice Sue....i'm gonna "stick" with the tape...