gombeen99,
+1 what everyone else has said plus allow me to hit the nail on the proverbial, since you seem unsure of what your position in law might be or what exactly this building is.
If the following is true as you say,
"there is no bathroom, kitchen or heating system, with some plumbing work to be done" then the building is not a house.
A house is defined as being "habitable" and washing, eating, and heating facilities are required as a minimum for any dwelling place.
It is very unlikely that there is an Opinion of Compliance since it is not habitable and therefore not fit for the purpose.
It is not complete or compliant with the Building Regulations and the long vacancy may have caused problems.
Any Architect's Opinion of Compliance that may be offered is likely to be qualified or misrepresentative.
Accordingly, it is unlikely that any financial institution will advance a mortagage.
Thus, unless you are buying for cash this purchase cannot proceed.
Please think twice and walk away.
Do not pay cash for this house.
ONQ.
[broken link removed]
All advice on AAM is remote from the situation and cannot be relied upon as a defence or support - in and of itself - should legal action be taken.
Competent legal and building professionals should be asked to advise in Real Life with rights to inspect and issue reports on the matters at hand.