Thanks for your replies.

I’d had a look at just releasing the gib.  Removing the allen screw adjusters does not release the strips, even if it did and they dropped out I would be left with a knee plus attachments no longer retained by its slides but just balanced on its feed screw, no go.

In the end I removed the table and cross slide which allowed me to clean and lubricate them.them.  I could not shift the allen screws holding the vertical feed to the underside of the knee so had to release the head to column locating pins and three of the bolts then turn it around a little to get the horizontal spindle out of the way so that the knee plus its feed screw could be lifted off the top of the slides.   Once off and inverted I could release the allen screws holding the feed assembly to the knee.

The main problem was swarf all around and under the gib strips.  The two allen screws which hold the strips to the knee and should allow some movement when adjustments are made were very loose and the bottom of their sockets not perfectly flat so the strips moved as the direction of travel changed hence the jamming.   Once cleaned up, fitted correctly, lubricated and replaced the action is good.   There is just some increase in tightness right at the bottom of the travel.

Thanks again for your help, Chris