Up the creek without a.....signpost

Lisa and I attempted to walk the circular route at Martlesham Creek this morning.  It's not one we've tried before. 
We had walked about 7 miles when the footpath petered out at the edge of a meadow - no signpost, in fact no sign of a footpath in any direction.  We re-traced our steps back across the field looking for a signpost that we may have missed, but there was none.  So we had to give up and go back the way we had come.  It's a mystery!