Ommercial Property law: termination of lease and Forfeiture of lease

This is a problem question where bela a fellow lawyer needs advise on the area of law stated in this letter. Please include the law s17 (notice) landlord and tenant act e.t.c, covenants: whether qualified or absolute covenant. close reference to the application of the relevant law, statutes, cases to back up statements and articles as references. references should be listed as footnotes, use as many references that can be used. please focus on the issues raised and not generic issues thank you. the question is mentioned below:

Bela, a practising barrister, has asked for your considered opinion on a problem that has been causing him concern.Give your advice on the problem he has set you:

Abstract of facts from Bela: In 1995, , Monster Properties plc granted Chillers Ltd a 25-year lease of a large retail unit for use as an insurance agency. Chillers Ltd covenanted, inter alia:
to pay the rent of A?700,000 per annum, subject to a review in the seventh and fourteenth years
not to alter or add to the demised premises
not to assign without the consent of Monster Properties plc.
The lease also contained a forfeiture clause, which operated by way of a provison of reentry, properly worded to cover breach of any of the covenants in the lease, including the covenant to pay the rent.
Chillers Ltd, with the consent of Monster Properties plc, sold the lease to GhostsRUs Ltd, who sold the lease on, again with consent, to Frighteners Ltd. Frighteners Ltd covenanted directly with Monster Properties plc to pay the rent reserved in the lease at the time and in the manner therein set out. Frighteners Ltd, in breach of covenant, extended the premises, increasing the floor space by 10%. Monster Properties plc condoned the breach, and the additional floor space was taken into account on first rent review, resulting in the rent being increased to A?850,000, A?30,000 more than it would otherwise have been.
In January 2013, Frighteners Ltd later assigned to Spooky Sales, without seeking the consent of Monster Properties plc. Monster Properties plc then sold the freehold reversion to The Vault plc in February 2013.
Spooky Sales has recently been facing real financial difficulties, and have been unable to make the annual rental payment of A?850,000,due last month

Bela seeks advise for The Vault plc as to any rights they might have in this matter to
recover the outstanding rent (and from whom). They want to know, in addition, what procedures they should follow if they elect instead to forfeit the lease for breach of the assignment covenant or the covenant to pay rent. Clearly, they also want to know whether the forfeiture actions would be likely to succeed.

Also, and this is purely for my interest, would your advice in this matter differ if Spooky Sales had gone into insolvent liquidation and the liquidator disclaimed the lease?

please include references as footnotes where necessary as you need to back every statement you make. also i would need a bibliography,Thank you very much. contact me in case of anything