If the Will is lost, a grant of probate may still be made on a lost (copy) Will with an application to the Supreme Court.
You can oppose that order being made if you believe the Will was destroyed by the deceased intentionally revoking it.

If the Will is damaged?
Although small issues such as paperclip marks, a Will that has been re-stapled or small imperfections can be easily explained, they will need to be explained in detail before a grant of Probate is issued.

Additional marks made by the deceased on the Will after it had been signed may require an order from the Supreme Court to allow the grant to be made.
Damage to the Will may be so great that the Supreme Court will assume that it was intended to be revoked by the deceased. Evidence will be required to rebut that presumption and obtain a grant of Probate on that Will.

Has the Will been completed properly?
A Will must be signed in accordance with the Wills Act 1936.
Signed by the deceased in the presence of 2 or more witnesses present at the same time.
The deceased must have intended the document to constitute their Will.

If it is not complete, then questions will arise as to whether the document is a Will at all. An application to the Supreme Court may be required to obtain the grant of Probate.