Mystery Teal ID

I was out birding around the Heslington East campus lakes in York and came across three ducks that I didn’t recognise. They very much resembled a Eurasian Teal in size and shape, but they had a prominent off-white / buff cheek and had a dark blue (almost indigo) wing patch. Does anyone have any thoughts what these may be, and are these possible escapees or wild birds?

Thanks for your time! (sorry for low resolution photos, taken on a phone camera)