What would happen if there was a tie vote voting for a party?

I'm not sure quite what you're asking, but if in a British election the top two candidates get the same number of votes, the law prescribes that the result is decided by lot, by any method of the Returning Officer's choosing. The Returning Officer is the person in charge of actually running the election. So the election can be decided on the toss of a coin, the drawing of straws, cutting a pack of cards, or any other way of making a random choice.

This does in fact happen from time to time in elections for local councillors because the number of voters is smaller. In some parts of the UK there were local elections on the same day as the general election last Thursday (I had one white and one yellow ballot paper because of that) and in one local election in the west of England, two candidates got 1,878 votes each. They recounted three times and the result was confirmed. So the Returning Officer conducted a raffle - he wrote both names on separate pieces of paper, put them in a ballot box and pulled one name out blind to decide the result.