We've been round in circles a few times and back again, and a decision finally made - a risk perhaps but would like to think a calculated one:
Having checked back the planning consent does enable us to add a little more concrete but nowhere near all the areas concerned. We cut back originally due to cost and still a non-starter as works out so expensive!
We were at one point convinced digging out, membrane & aggregate was the best solution - coarse sand where horses are moved & crushed concrete for vehicle access which we have used previously. However, could be a risk planning wise, and chances are it wouldn't be granted if we did apply due to jobsworths, idiots and ridiculous policies - and would cost a whole lot more removing it if ordered to. There will always be a small handful of morons likely to be watching and ready to complain to the planning office. This option was also going to be very labour intensive as 8 wheeler tippers wouldn't be able to access directly to the space so would mean a lot of barrowing or expensive plant hire.
We had originally dismissed grass grids as seems they are only as good as the preparation etc and the need to bring in gravel / topsoil.
However, we have decided to run with the one we found that can be pushed into the existing surface with a vibrating roller. No digging involved, changes, or additional aggregates required - will be invisible almost. We were very sceptical, but have been trying a sample and even just one grid on it's own have been astonished how well it seems to be working. Got the chap who delivers our hay to run over it in tractor in a reasonably wet area - didn't sink below surface or break. Order placed for 138m2 of it - with the cost of the roller hire on top not cheap, but less than the mudcontrol mats and guessing about the same as the aggregate option, quite probably less when taking into account time/work. Not recommending it yet - all fingers crossed for next winter! Will report back with the results..............
We will hopefully be digging out the swamp where the tractor turns and loads the hay into the 'tiny barn' (aka as a stable with a double back door) and chucking crushed concrete / stone in over membrane - that would be pushing things too far I think for any grid! Would be great however if we could just tip a load of stone / hardcore / crushed concrete straight into the mud - been trying to convince myself this might work, but in theory and based on everything you read or hear not a good idea or going to last long. Anyone tried / direct experience? Tractor running over it just once a week throughout winter.