Because mine seized up, I "bent" the link rod, which no Park and a new link rod from and fitted by LR .
Experience is the only genuine knowledge, but as time passes, I have forgotten more than I can remember
Volvo V70 P2 2006 2.4 Petrol 170bhp Estate SE
MG Midget Mk1 1962

Previous: L322 Range Rover TDV8 3.6 2008; L322 Range Rover TD6 3.0 2002; P38A Range Rover V8 1999

Recently I lubed the cable are under the box and only did this as park was not in reach of the engagement process , now Park was easily obtained for a limited period and it slots in but only get reverse. So things I can only guess is that perhaps the cable clamp , without looking at it is required to release the forward position.
That being that the lube has hs finally released the proper position . Hope someone can see what Zi mean .

Got the beast up on a ramp at the moment , can anyone tell me if the joint at the end of the gear selector cable is meant to swivel with the arm to the gearbox please.

From the workshop manual,

Selector Cable
The selector cable is a Bowden type cable that connects the selector lever to the manual selector spool valve. A ’C’ clip secures the outer cable to the selector lever assembly. The inner cable is secured to an arm which is connected to the selector lever via a 'U' shaped bracket and pin.
The transmission end of the outer cable is secured to a bracket on the transmission by a clamp nut. The transmission has an operating lever which is attached to and operates the manual selector control spool valve. The inner cable is attached to the operating lever by a clamp bush and locknut. The clamp bush allows for the adjustment of the selector cable.

After trying some adjustments, I can see what’s happened there is a sheath supporting the inner cable when it’s extended into P , so this should be held back by the next clamp back and has slip to hold it in place , well this is broken or rotted away, tried tying it back to support the inner core but it gave way .
How difficult is this cable to replace and has anyone done it.

Looking at RAVE, the centre console has to come out. The outer cable is held in place at both ends by sliding washer/clips, and the cable has to be withdrawn "into" the car.

Most difficult part getting the centre console out and back in again.

Most important part is keeping the selector arm in the right place when tightening up  .
Experience is the only genuine knowledge, but as time passes, I have forgotten more than I can remember
Volvo V70 P2 2006 2.4 Petrol 170bhp Estate SE
MG Midget Mk1 1962

Previous: L322 Range Rover TDV8 3.6 2008; L322 Range Rover TD6 3.0 2002; P38A Range Rover V8 1999

What exactly has broken or rotted away?

There is a sheath over the cable that slides ove the the extreme end of the cable , this supports the inner section fro bending when D to P is selected.The sheath has a flanged end which I think is attached to the u clamp and held by the clamp to support the cable . The flange has rotted away , so when Park is selected or any forward motion the inner cable buckles .

If you look at the last picture I tries to hold the broken flared end with tying wire but it just allowed the tube to run with the cable .

Oh, and RAVE says put the gearbox in PARK before you start. That will be fun if your entire problem is not being able to get into PARK

You may have to have a helper pull on the selector rod to get it there. .
Experience is the only genuine knowledge, but as time passes, I have forgotten more than I can remember
Volvo V70 P2 2006 2.4 Petrol 170bhp Estate SE
MG Midget Mk1 1962

Previous: L322 Range Rover TDV8 3.6 2008; L322 Range Rover TD6 3.0 2002; P38A Range Rover V8 1999

Yep , I can select park from below when I straighten the cable and push the selector arm forward , however because this sleeve moves out of place when I do it .

I am hoping the end section which is broken with corrossion is simply replaceable on it own and I can slide off the old and replace with newor s/h .

Can anyone identify for me that a V8 gearbox cable off the same age is the same as a TD6 CABLE, this I can get s/h.

Rather than replace the cable you could consider fitting a wire cable clamp and washers to the cable sleeve either side of the fixing bracket.
If you measure the diameter of the sleeve it should be able to get a couple that are a tight fit.
I don't doubt a couple of these in place would stop the cable sleeve from moving. Just don't over tighten them.
Certainly something I would try before fitting a new complete cable.

Thanks I get the jist of your suggestion, you mean something like a jubilee, although this might be too small for that, maybe cable ties and a washer on the sleeve?
Have you pic of the wire clamp you mean please.

Try EBay item number eBay Item No. 182448759217.

Ah of course, thanks I’ll give it a go.

You might need a good few washers to pack out the cable sheath next to the clamps to ensure you are on solid material away from the corroded bit.