Is it an error or a badly made fake?
Initially it looks like an off centre strike. Does it have the micro lettering? Compare this coin against another, looking at the tiny lettering on both sides just inside the bevelled edge. A close up photo might help.
Your coin has what appears to be a die crack on the reverse (tails), which is curved across the lettering "E PO" of "ONE POUND". This reminds me of one of the telltale signs of a known fake. Google the fake pound coin database for more details.