I have now finished taking off the anti-woodpecker plastic sheets and removed all mouseguards. I have also spread salt on the ground to act as a natural weedkiller. 
Today was a perfect day to observe hive entrances and it was clear that the poly hive had not survived.
I did a hive autopsy and looked carefully at the dead bees for deformities etc. however it looks like they starved from the way they had clustered around the outer quarters of the brood comb.
Looking at the hive record, although they had fondant, they had not taken it down from early January and this is when I think their numbers became unviable.
I will now clean the hive with washing soda and take the good brood frames home to freeze for a few days and then return to the apiary for re-use.
If the hive was wooden I would have flamed it.  
There are possibly two more hives that are weak but I did not do a full inspection in case I chilled them too much.  
I prefer to open hives when I am comfortable in a t-shirt under my suit and it was still too cold for that. 
I will look at splitting the stronger hives to form nucs next month and I will use these to re-start any empty hives.
Splitting means waiting for the queen in a hive to build upto 7-8 frames of brood and then we take her, plus 2 frames of brood, 2 frames of stores
and an empty drawn frame and loads of bees shaken into a nuc.
In the hive, we make sure we leave a couple frames of 1-2 day old eggs, stores, and replace the taken frames with drawn. The nuc will be fine as they have their queen.
Any foragers in the nuc will return to the hive and hopefully in 16 days time we have a new queen emerging who will then get mated and keep the colony strong in the hive.
Meanwhile we have a slowly building nuc that we can then transfer into a hive after a few weeks.  
Last, I went to Beetradex at the weekend and splurged on new wooden framed queen excluders so if anyone would like to buy some cheap metal and / or plastic QE’s -  I have several for sale.  £1 each.  

Moira
Apiary Manager