Having mapped many of the streets of Teignmouth today I hadn't realised I'd performed a miracle - see map.

There are possibly three explanations:

1) my gps was giving me false readings

I checked it against Garmins GB map and the track more or less was spot on.

2) the tide was out

Could be, but it has been out ever since I moved to Devon (35 yrs)

3) the osm coastal data is not 100% accurate or up to date.

I wonder...