Class Q planning granted on working farm

[George from SJM Planning]

My understanding of Class Q and have done two is that the buildings need to have been redundant for over 10 years and not in use.
Class Q will not get you full PP until the building is converted to residential then you might be able to knock it down and build a new build. I had this which is crazy as one of the buildings would cost £600k to convert but the same building as a new build would cost £250k. If the building falls down during conversion all permissions are lost.
Also Class Q only gives you a residential garden the same size as the footprint you are converting. That area must be all round the building otherwise the land is deemed as agricultural.

The buildings do not need to be redundant and can be in use right up until the conversion.
You are correct that Class Q does not give you planning permission but it does provide a material fallback position to 'trade' when applying for planning permission. There are numerous cases where Class Q has been traded for dwellings built on a totally different footprint.
Class Q does only give you a curtilage equivalent to the floor area but this can be extended with a change of use application once the Class Q has been implemented.