On our site,
1. I contact the individual plot holder concerned either face to face or telephone and ask what their future intentions are with the allotment.
2. Sometimes they just give up the allotment and admit they no longer have the time for it. Or we agree a reasonable timeline to rectify the problem. I then record this conversation on file for reference. They are informed this will happen. Usually this is suffice.
3. If after the agreed timeframe things are not rectified, a 28 day written warning is sent recorded delivery. This states if the errors are not rectified within 28 days then an eviction notice will follow.
4. If no progress has been done by the 28 day point, we then send the eviction letter giving a further 28 days to clear any personal belongings.
5. On the 29th day, I reallocate.
If things are rectified within the 28 day warning period, that is the matter closed. However, each plot holder can only go through this process 3 times after which they are evicted without reprieve. We have never got to this stage though as usually one letter is a sufficient shot across the bows for tenants to maintain their plot.
All the above, except the initial 'informal' conversation is clearly written within the terms and conditions of the tenancy agreement.