What is this chair?  

If none of our UK members identify it first, ask Angela Linforth.
The magazine was acquired by Immediate Media in 2011, three years after your issue was published, but there might still be someone there who knows. Email the magazine's editor and see whether you can charm her into searching for the information:
dearangela at immediatemedia.co.uk

Try
researching 'Ben' chairs from Yugoslavia.
I'm not 100% certain, but it's a good place to start.

Chair ID
Hi,
The chairs were designed by Oswald Haerdtl for Thonet, Vienna. I once had the opportunity to buy 30 (!) of these chairs in Austria. All sold..
Kind regards, Judith

Ah, thank you so much Judith!
Ah, thank you so much Judith!

Check the link below
Check the link below, looks similar although hard to tell without a close up of your image.
http://www.ffenss.com/listings/show/281

Aha!
Aha, I can't believe these are Day chairs after all! Should have guessed as I love his work the most, but I never knew he designed these. Thanks for solving a long search! Just wish I had the money to own one.

I'm
not convinced by that attribution.
It is based on it looking 'similar' to a Stamford chair.
The Stamford, designed in 1952 was fully upholstered with metal legs. The armrests were much wider (and integral) and the back wasn't cut out.
In my opinion these are definitely not by Robin Day.
The attirbution further up the thread (that of Oswald Haerdtl for Thonet) is the correct one.
See link below.
http://tinyurl.com/86hflwr

But what about this?
I thought so too till I saw the label 'Designed by Robin Day No. 006732'. - see here:
http://www.johannapinder-wilson.com/index.php/catalogue/furniture-and-ob...

Robin Day's design output
is fully and concisely catalogued, this chair is not by him.
I can only assume, therefore, that the label is faked.
There are, though, hundreds of attributions for it as by Oswald Haerdtl.. and only one for Robin Day.. hmm
Here is the Robin Day Stamford series the seller is likening it to (but can't give a model name or number)
please forgive the poor quality.
It's quite a different chair altogether.
http://www.lichterloh.com/en/1991

Is it Robin Day sans upholstery?
Is it possible that this is a Robin Day chair that has had its upholstery
removed? I can't imagine why anyone would bother faking a Robin Day sticker.

thonet - Oswald Haerdtl http://www.zezschwitz.de/onlinecatalog.php?id=61&chapter=2&action=langua...
The Thonet chair without the armrests is also very nice:
http://www.von-zezschwitz.de/detail.php?onlinecatalog=1&chapter=4&object...
Happy with these 4:
http://pinterest.com/pin/96123773267879689/

Pontificating opinion
In response to the pontificating opinion of Robert1960 (UK) above:
I purchased the chairs from a reputable auction house where they are catalogued as such and where I have the receipt as such. They bear the Hille label and Robin Day's name, as I photographed.
Be extremely careful when stepping beyond your knowledge and expressing your opinion of 'I can only assume, therefore, that the label is faked'.

.
Is that really a Hille label though?
Looks nothing at all like the normal one.........

JPW
I'd say all the proof you need is in the links posted by others where you can see pictures of both chairs, I'f I had to make a choice I'd say your chairs are by Thonet!
Perhaps you should take up your grievance with the auction where you purchased them armed with the relevant pictures.