Jack Purvis & Kenny Baker Autographs on Double Bill Poster

Hi,

I've got a British 30x40 inch quad poster for the 1982 double bill of Star Wars & The Empire Strikes Back, signed by Jack Purvis and Kenny Baker.
Not sure if there any autograph experts on here, but I would be grateful if anybody could authenticate/value these signatures and poster.

I understand Jack Purvis' signature is a bit of a rarity, so any help would be appreciated.

The signatures date from approx. 1990 and were obtained through a work colleague, who was a family friend of Kenny Baker.




Many thanks,
Jon

Finally added photos.
Any help with authentication of signatures and valuation would appreciated.

Thanks.