Section 146 on Long Leasholder

I manage a Freehold where upper parts are on a single long lease [125 years] and the Leaseholder has split it into four flats. There is now a leak for around a month from one of the flats into the shop of ground floor. The long leaseholder is not repairing it and so is the sub-lessee not repairing.

Can I serve s.146 notice on the long leaseholder? do I have to send a copy to his subtenant?

Where can I get a s.146 template?

It's more complex than that. Where a s.146 Notice replies on disrepair, it must take account of the Leasehold Property (Repairs) Act 1938** too. I'd not suggest DiY these procedures!

** See http://www.legislation.gov.uk/ukpga/Geo6/1-2/34/contents

Here's s.1(4) for a start, with my underlining:

A notice served under subsection (1) of section one hundred and forty-six of the Law of Property Act, 1925, in the circumstances specified in subsection (1) of this section, and a notice served under subsection (2) of this section shall not be valid unless it contains a statement, in characters not less conspicuous than those used in any other part of the notice, to the effect that the lessee is entitled under this Act to serve on the lessor a counter-notice claiming the benefit of this Act, and a statement in the like characters specifying the time within which, and the manner in which, under this Act a counter-notice may be served and specifying the name and address for service of the lessor.