We have featured a William Plunkett WP01 sofa of this style in the past, which sells new for just under £3,000. So you can see how much of a bargain these William Plunkett lounge chairs could be.
Presumably from the same era as the sofa, which makes it a mid-60s design, the chairs can be used separately or combined to make a modular seating unit. All have heavy metal frames with a white finish and what's described as 'leatherette bubble cushions'. I would have thought an original Plunkett would have been leather – you might want to check that out.
If it is a genuine Plunkett design (and the seller is retailing it as one), the current price of £50 per chair is something of a bargain.