This is why other jurisdictions have begun to limit these kinds of versions that are invented on the stand. If you don't disclose this kind of version in interrogation, it can lead to an adverse direction by the Judge to the jury
Under Section 34 CJPOA 1994, (Failure to mention facts when questioned): If a suspect fails to mention a fact during police questioning that they later rely on in their defence at trial, a court may draw an inference that the fact was fabricated later.
An Act to make further provision in relation to criminal justice (including employment in the prison service); to amend or extend the criminal law and powers for preventing crime and enforcing that law; to amend the Video Recordings Act 1984; and for purposes connected with those purposes.
www.legislation.gov.uk
It's a sensible reform IMO. As you can see here, the CW was prevented from investigating a critical fact claimed by the defence. The day was saved at the 11th hour - but there is really no need to allow defendants to do this without negative inference.
IMO