I'll start by acknowledging that I went wrong in the first mile and move straight on to blaming my watch! Most watches, I think, just show you the route, the map or the direction you should be going, mine requires you to be at the precise start point before it will reveal any of this to you, otherwise you just get a direction arrow pointing you in the direction of this point with the distance you have to get there, once there it'll show you the route. The GPX for this route from the Hayling side starts in the sea, I couldn't reach it from the pontoon so had to give up on any watch directions and follow the signage , the signage is pretty rubbish, non existent where you need it and plentiful on long straight trails where there's no options other than to go ahead.
I followed the trail sign taking me off the road without realising that I should have rejoined it almost immediately rather than following the path round, this detour extended the route and had me running on shingle and marsh rather than road so will hopefully be seen as a penalty and allowed.
The remainder of the route follows the bulk of the Portsmouth Coastal Marathon route and is familiar to me, on a Sunny day like today it's a really pretty route with great views of the harbour.
The sea wall has completely collapsed about 6 miles from Hayling and whilst it is completely dry at low tide I'm not sure how passable it is at high water, you'd certainly get your feet wet although only for a few metres.
The route was run solo carrying any water I required