Can roosting pockets replace ivy for winter use? Who do I ask to put up bat boxes on a tall tree?

Due to unfortunate circumstances I have had to remove all the dense arboreal ivy from my Ash tree as it was beginning to negatively affect the tree, and as the tree itself was already overgrown the tree surgeon topped it thereby removing the canopy. I feel so guilty both for destroying the bird's homes - I'm pretty sure I saw nesting wool hanging down from a now exposed branch - and for damaging the tree because I didn't know that he would pollard it. Now the blue tits, great tits and robins are possibly without a cosy natural winter home and are completely exposed when they come to eat from my feeders; I've noticed a sharp drop in visits in the past few days. I want to rectify this massive mistake by making sure that the small birds survive the freezing winter nights and want to know how I can do this. I've ordered 6 roosting pockets made from reed grass and thought that if I put them on the tree then the birds can stay warm in them, is this line of thinking correct? I live in London so winters are usually mild but there is always a chance of a really cold snap.

Also, in summer I saw one or two bats flying around during the evening so they may have been using the ivy as a summer roost. I'd like to put up some bat houses to help the bat population but the main obstacle is managing to secure them to the tree high up. Who can I ask to install the bat boxes properly without paying extortionate prices?

This shows what the tree/ivy was like before and what it is now:

I'm sure many would consider this a crime against trees. There is some ivy left along the fence for what it's worth but that is kept under control.

  • Re it being an ash tree, Was it checked for 'ash dieback'? The disease is everywhere here, and loads of trees are being felled.
    Re trying to replace a mature native tree, very difficult. I don't know enough about roosting pockets to comment other than to raise doubts about hanging them out in the open.
  • In reply to Robbo:

    It wasn't checked for ash dieback and according to the map of reports, my town hasn't been affected yet although I'm sure that's just because no one's reported it. Only thing I can say is it is 100 years old and had a full and lush canopy this summer.

    Re: hanging pockets in the open, I was thinking securing them to NE facing trunks so they're not swinging freely and are out of the wind