No doubt both partly inspired by the increased public interest in plant-based diets, and partly (I suspect mainly) inspired by increased consumer desire for 'allergen free' products, there are now a few dairy-free butter substitutes widely available in mainstream supermarkets.
There are two I don't really use myself, but worth mentioning: Vitalite, which has been going for years here in the UK (slightly older members will remember the catchy 80's Vitalite advert featuring dancing sunflowers - see below), is one. I used to have it as a kid, but haven't really used it in adulthood much. A newer one has come out recently by Flora (called Flora Freedom) and I haven't tried that so can't comment, however the reviews I've seen look good. It's a bit more expensive than either Vitalite or Pure, but may be worth trying.
However our personal long standing favourite for some time now is Pure. You can get it in Sunflower, Olive and Soya versions; we prefer sunflower as it seems to melt a bit more easily and comes out of the fridge spreadable (though not super soft).
Costwise, Vitalite is a bit cheaper than Pure and from what I recall of eating it, is probably worth trying (currently only £1.20 for 500g - so great if you're on a tight budget), however Pure has the most inoffensive ingredients list (no trans-fat containing emulsifiers). Currently in ASDA Pure is £1.50 for a 500g tub which is still 25% cheaper than the very cheapest dairy butter available there (currently £1.99 for the same weight block of 500g).
Top Tip: sprinkle a little crystalised sea salt over your spread after it's gone on potatoes or on crackers, and you immediately have something that tastes almost exactly like dairy butter. Sea salt for preference as it melts sweetly in the mouth, really enhancing the buttery effect.
Anyway, the bottom line is it's both easy and cheap to source vegan friendly spreads in the UK today.
Pure Sunflower ingredients:
Water , Sunflower Oil (35%) , Vegetable Oils (Palm, Linseed) , Salt (0.75%) , Flavouring , Vitamin E , Vitamin A & D , Colour (Carotenes) , Vitamin B12 .
80's Vitalite advert: