It no doubt is. But it's there and you have a large community of gamers standing their ground despite PS4 offering the better deal and taking the lead.
360 managed to dig itself in the UK pretty deeply.
TBH I've never fully bought into the idea UK was Xboxland last gen. Both consoles were strongly advertised throughout and if you actually factor in early 360 launch I'm not sure they were that far apart.
Don't get me wrong 360 was more popular but it never felt to me in UK (nor from the data) that it truly dominated.
The final split I remember seeing was around 61 to 62% for 360 and 39 to 38% for PS3 (from Nintendo material shown here on GAF). Now that looks good for 360 but it includes two extra holiday periods of training plus around 16 extra months of sales. Factoring in PS3 "lost sales" compared to this gen I'm suspicious that the underlying weekly averages, while definitely favoring 360, were closing than many assume. If they'd launched more or less same time (as with PS4 and XB1) then the final split would clearly have been closer, say 55% to 45% for 360. A good win but hardly dominant and with plenty of room for PS brand.
In the end I think UK buys both brands pretty well and who "wins" is driven by price, deals and perception. Right now while PS4 is doing great in UK for example the XB1 is clearly selling okay with a likely ratio (if I read other posts correctly) of around 1.25 to 1.3 advantage for PS4.
I just don't think UK, PS2 gen aside, has ever been Sonyland or Xboxloand since PS3/360 launched. Both can sell well here, as with US, and both seem to be selling well enough both HW and SW from what I can see in charts.
I'd love to see someone from sales GAF actually estimate what the final split PS3/360 would have been if they launched same time and PS3 got those additional 16 months or so plus a couple more holidays. That would give an interesting view into the true underlying demand for each vs the actual results that include an artificial (i.e time to market induced) lead.