You can start off by asking
Why do the debt collection agencies/baliffs refuse to show copies of the deed of assignment or the novation?
Why they do not hold the original contract agreements, unmarked, unstamped and unaltered in any way? This because they do not have them.
If they are buying debt in pennies in the pound why wasn't the original borrower contacted for settlement first?
Where is the bilateral signature establishing a contract between the two parties? There isn't one period
The theft act 1968
17 False accounting.
(1)Where a person dishonestly, with a view to gain for himself or another or with intent to cause loss to another,—
(a)destroys, defaces, conceals or falsifies any account or any record or document made or required for any accounting purpose; or
(b)in furnishing information for any purpose produces or makes use of any account, or any such record or document as aforesaid, which to his knowledge is or may be misleading, false or deceptive in a material particular;
he shall, on conviction on indictment, be liable to imprisonment for a term not exceeding seven years.
(2)For purposes of this section a person who makes or concurs in making in an account or other document an entry which is or may be misleading, false or deceptive in a material particular, or who omits or concurs in omitting a material particular from an account or other document, is to be treated as falsifying the account or document.
Also check out the fraud act