......My understanding is that at some point during F/TF production, an improved Head Gasket design was introduced to deal with the problems experienced with earlier cars
There were various revisions made to the elastomer beading of the SLS/elastomer head gasket over the production lifetime of the K series engine, none of which appeared to make any measurable difference to the incidence of HGF.
MG Rover engineers were working on a completely new multi layer steel head gasket (MLS) when MG Rover went bust, and work on finalising it and bringing it to the market was carried out under the direction of the administrators of MG Rover in responce to demands from Land Rover, and I believe funded by them. This MLS gasket was first introduced as a replacement part through Land Rover dealers in early 2006, and it became available through XPart as a genuine MG Rover part shortly afterwards. However, whilst certainly a big improvement, they are not a 100% resolution to the problems.
SAIC also developed a new multi layer gasket for their reverse engineered and improved versions of the K series engine which was used in the MG6 and Roewe 750. The same gasket was also used in the China produced MG3SW and MG7, as well as the China manufactured TF.
Obviously, neither of these MLS gaskets was ever fitted originally to an MG Rover car, but many that have suffered HGF have had the Rover/Land Rover MLS fitted during the repair, and some have had the SAIC six-layer MLS fitted.