I had a look through their old press releases and couldn't find a reference to the .tv domain.
On their site it doesn't mention marksandspencer.tv though, they call it "M&S TV", that looks to be the the brand.
Interesting about the youtube channel (which has one reference to the .tv under each video), though it looks like it is getting very little traffic, around 130 subcribers/30k views compared to the claim of over a million views for M &S TV. Even then if you play the videos it says "for more go to marksandspencer.com" at the end.
Saying "all links point to the .tv" isn't accurate either, the only actual link goes to the .com. Each video in the description references the .tv though, without having a functioning link. Effecively on that youtube channel they interchangeably use the .tv and the .com.
Looking at compete also it looks like the .tv is getting about 20 visits per day,
Site Profile for marksandspencer.tv (rank #1,658,419) | Compete
Alexa looks better,
marksandspencer.tv - Site Info from Alexa
Though if you look at that Alexa data 95% of traffic is just from people loading videos via the .com site, not people who actually visit the .tv.