Looking at any party that got at least 47,223 votes, we see:
|Party||Seats||votes||votes per seat||seats under PR|
|Ulster Unionist Party||2||114,935||57,468||2|
|Social Democratic & Labour Party||3||99,809||33,270||2|
|Scottish National Party||56||1,454,436||25,972||31|
|Democratic Unionist Party||8||184,260||23,033||4|
(updated to reflect final score - the single "other" seat is left off of this list)
Doesn't look so good for UKIP, at 3.8m+ votes per seat, does it.
The system does seem to be set up to ensure that the bigger parties cannot be challenged.
For the record, the PR figures above assume that anyone getting less than enough votes for one seat would be ignored, and the seats split among the remaining parties according to vote share.
Interestingly, these PR figures would still leave Conservatives and UKIP 1 seat short of a majority if they worked together.
Someone at Tim's place mentioned that UKIP have more votes than Lib Dems and SNP put together - something to think about!
Numbers taken from the BBC page at http://www.bbc.co.uk/news/election/2015/results