[Folleyl]

Our chickens haven't recovered their feathers since moulting and 3 of them have bald backs . They are still laying and seem fine but look awful.
The cockerel does favour these hens is that what is keeping the feathers from growing back?

[Roughlee Handled]

Our chickens haven't recovered their feathers since moulting and 3 of them have bald backs . They are still laying and seem fine but look awful.
The cockerel does favour these hens is that what is keeping the feathers from growing back?

He (the cockerel) is stopping the feathers from growing back. 
How many chickens do you have to your cockerel? 
Chicken saddles.
http://reviews.ebay.co.uk/Poultry-Chicken-Turkey-Saddles-by-Foxfield-Fowls_W0QQugidZ10000000001405250

[Folleyl]

we have 5 chickens

[Roughlee Handled]

That is your problem I think its ten chucks to a cockerel (that's the recommended amount).  You could either get some saddles or more chickens to take the "pressure" of the favoured ones.  You could also remove the cockerel.