Advice sought on action to take in an emergency situation

Maintenance

Can you give me some advice please - this is NOT in relation to a property I let; but a 1st floor small studio flat in a small block my step daughter rents in London.

Basically she is having difficulty getting the landlord to deal with emergency repairs required. Approx 1 week ago a window was smashed from falling material from the building roof. And as of yesterday the foul sewer is backing up sewage in the toilet pan and shower tray when flushing the toilet.

She has realised that high level guttering has fallen off the roof smashing an external foul pipe as well as her window. Worse still it has been discharging onto another tenants external yard below but that tenant seems to have adopted 'self help' by taping and sealing the broken pipe over now causing the backing up into her flat.

The landlord is reprehensibly proving very elusive/non contactable.

His jobbing contractor sent round to look at the window has not returned to site for some days.

What can and should she do please?
The flat is bluntly currently unfit for habitation.
What exactly can she reasonably call upon the landlord to do and in what time scale? What action can she reasonably take if the landlord does not act promptly.
Although she does not really want to move (she has been there 2 years) the landlord is terrible and she is tied into a lease until end Sept 2013 and has paid a hefty deposit (and i guarantee her obligations)

Advice welcomed/needed urgently please!