I'm not entirely sure as my route was quite 'out and back', but I do remember from Street View that it looked like a clear route to Burnham was possible, albeit a little inland.
Ah, I see.
I've done the run you describe - via Wallasey Island - a number of times. But I'm pretty sure it is no longer possible on account of the robust gates which have been installed half way between Tillingham and Burnham on Crouch .
I'm not entirely sure as my route was quite 'out and back', but I do remember from Street View that it looked like a clear route to Burnham was possible, albeit a little inland.
https://www.strava.com/activities/9410662713
If I had longer I'd have considered heading down there and getting the mini ferry to Wallasea Island and come back through Southend etc.