Before Ilford's management buyout some years ago, Ilford Imaging UK Ltd, as the company was then known, did have at least one colour negative film made for them by Ferrania in Italy. It was called Ilford Ilfocolor 100 Plus. It seemed to be made for certain markets only, not the UK. I did however manage to buy a few rolls, some of which are still sitting in my freezer with an expiry date of October 2002. So my guess, and that's all it can be, is that the Ilfochrome slide film spotted in Turkey is of the same era. Today Harman in the UK can only use the Ilford trade mark for black & white materials. The only other possibility, is that the Ilfochrome film was made by Ferrania for the Ilford concern in Switzerland which makes Ilforchrome paper & inkjet paper. But as Ferrania have confirmed they don't manufacture slide films anymore, that seems extremely unlikely.
Going further back into the past, in the 70's & 80's, when Ilford had ceased to manufacture its own colour films, it still wished to have a range of colour films on offer. It therefore sold print & slide films rebranded as Ilford. First they were supplied from the Konica factory, at which time Ilford ran a processing service for the ISO 100 slide film, and then later they came from Agfa. Some of the latter were even sold in 120 rollfilm format. I bought many, and looking at the edge markings, although marked Ilford, it is not difficult to work out which factory they originated from.
As to the original post, if you want to shoot on UK made colour film, then realistically, unless you want to use hopelessly outdated materials, then it would be a case of hunting down some UK Kodak made films. I think they were made here until sometime in the 1990's, or maybe a little bit earlier. Most of the range were made here at one time, until gradually they were replaced by versions made in factories overseas. Before that, you are going back to the long ago days of the 50's & 60's, when Ilford made its own colour slide & print films here, and in the 50's you also had things like Dufaycolor & Pakolor, and even Woolworths sold a colour print film under the Standard brand, but probably made elsewhere. The last UK made Ilford colour films were made in the late 60's/maybe early 70's for the TrifCa brand. This was a deal where you paid an all-in price for printing & developing (a triple photo - one big, two small) & got a replacement TrifCa film. But even if you could find one, Ilford's process was slightly different to the C22 & Agfa processes which were in use then. And the negatives had a distinct yellow mask, rather than the orange or brown we are used to today. To further confuse matters, some of the TrifCa films (in the UK) were supplied by GAF (formerly Ansco) & were C22 process. Best of luck and don't forget to use a Weston exposure meter!