Will tactical voting have a big effect on the UK General Election?

It has been a big talking point in the lead up. In England they're talking about voting for whoever has the best chance of beating the Tory candidate in each constituency, be they Labour, lib dem or something else. In Scotland the constitutional question is resulting in tactical voting with unionists voting for the Tories and on the nationalist side the Greens so far won't stand for 6 Scottish seats in order to improve the SNP's chances.