Repairing a firewall and the party wall act

[t1grm]

I need to repair the lead flashing on my side of a firewall on the roof of a Victorian terrace. It will involve hacking off the cement on my side, installing new lead and reapplying cement. Do I have to notify my neighbour under the party wall act before getting this work done? I was under the impression minor work was not notifiable. I would consider this minor work. From the party wall act:

 

"Some works on a party wall may be so minor that service of notice under the Act would be
generally regarded as not necessary.
Things like:
 drilling into a party wall to fix plugs and screws for ordinary wall units or shelving
 cutting into a party wall to add or replace recessed electric wiring and sockets
 removing old plaster and replastering
may all be too minor to require a notice under the Act."

 

The neighbour has got wind of what I am doing and has asked for written grantees that I will cover the cost of any impact on his side and is threatening to invoke the party wall act if I don't I don't want to write him a blank cheque as his side of the firewall is probably is as bad a condition as my side.