That may be because the Scots are tempted to send MPs to the UK parliament who concentrate on the advantages they can get for Scotland rather than the UK ?
That emphasis is ok for the Scottish assembly but hardly appropriate for a UK parliament.
UKIP (and indeed all the larger parties) aren't about just one part UK location and what it can do for the people there. It is trying to do what it believes is is best for the whole of the UK; so it has no unfair advantage over other parties. It has to get it's MPs from persuading the voters in each constituency by it's UK policies alone. That is how it should be, although it would be better if parties didn't exist at all, but traditional, incumbent to the constituency, parties are hard to shift.
That's not to say a representative shouldn't bear in mind the needs of those they represent but it needs to be kept in proportion to the job they are elected to do, which is run the whole kingdom not grab preferential treatment for their locals.