Smaller then a Dunlin, slightly smaller then a Blackbird
No interactions present.
Aploogies A bit out of focus, Camara problems
2 reasons why these are unlikely to be little stints:
a) they very rarely winter in the UK
b) 6 of them together is very rare any time of year
Also you say they were slightly smaller than a blackbird, which is a good description of the size of a dunlin. Size is very difficult to judge (I assume there weren't any blackbirds on the mud with them!) but little stints are sparrow-sized, much smaller than blackbirds.
The photo makes the birds look very reddish, but this may be inaccurate as both both species are grey at this time of year, as are sanderlings. On balance I'd still go for dunlin though, as these are by far the most common small wader.
Lat/Lng: 51.0, -4.1
OS grid ref: SS5430