Free Traffic Legal Advice

Advance warning sign here : -
https://maps.app.goo.gl/jJHxTG7UY21rejCW7
and here is the actual restriction sign: -
https://maps.app.goo.gl/DoavSTpy5TwJMPts5

I have to say I think it would have been better to have two signs, with the other on the traffic island, but the advance sign diminishes that argument. However the contravention time was night time, and with neither sign illuminated, one could argue the signage is inadequate. The trouble with this argument is that the council, (who out the signs up), will argue it is adequate, so you'd have to take them to the adjudicators and risk the full PCN penalty.

Thanks for the reply i really appreciate it. I believe i entered through a different area from Rodborne Rd.
https://maps.app.goo.gl/TvTpJsvaSYdRSZPR9

We thought we were turning into parking area for the shopping outlet but we didnt see the sign as it was dark. What do you think would be the chances for the appeal on the basis of inadequate signage if go ahead with the adjudicators?

Yes, it's confusing, even using GSV ! However, there is an advance warning sign: -
https://maps.app.goo.gl/xN2VwRF9Vb7aQRZa6
and also unequivocally on the traffic lights: -
https://maps.app.goo.gl/sxoNTEwSoXDhk7qy6

What you should have done is drive past those traffic lights and follow the signs on the large sign board after the traffic lights, to the other shopping outlet car park.
Sorry, but the signage, even though dark,  is there, and the traffic lights are obviously illuminated incl the No Left Turn sign on them.
You could try submitting an informal representation on the lines of unfamiliarity with Swindon, but councils have very hard hearts now, and, of course, keep all the fines money if they refuse reps.