do i need to remove the boards under my tiles?

Hopefully you haven't removed the boarding.

Question 1. NO don't remove the boards it is better to leave them if sound and contact your local council building control office for advice on alternative insulation batts set between the rafters INSIDE the loft space.
2. Yes they do add better insulation than open battened roofs.

You may even be able to staple the roof felt to the inside but go with what the planners say.

Bob
October 2010