House Martin Nests


I am about to knock down an old house and build a new one on the plot. 

I have about 15 House Martin nests under the eaves currently and we love having our annual visitors as they are amazing to watch as they swoop in and out of the nests (the nests are right outside our bedroom window), they make a lovely noise when the young arrive (but are silent at night !) and they seem to decimate the mosquito population every evening !!

I have two questions:

1) Now the nests are empty can I safely remove them legally to ensure they are not occupied early next year (when the demolition is due to start) ?

2) Are there any options to provide alternative housing for them next year whilst the build is happening and beyond (The new house does not have proper eaves).

Any advice gratefully received.