Roof Underlay - is a repair possible from the inside?

[Alex UK]

 

I have just discovered holes in my underlay as per pics. can this be repaired from the inside? if not what needs doing? how much should it cost? I still have scaffolding where the solar panels are. thanks a million

[Redbeard]

Is there anything wrong with the roof tiles? underfelt is only a second line of defence in case the tiles fail. I would not rush to repair this unless there's a leak. All the growth suggests that the tiles are not young, and it's impossible to tell from a pic. Would I be right in guessing 1960s or 1970s ish?