It not a question for a crystal ball. Gambling with your mortgage is foolish, (I would say stupid but the moderators might object).
As a general rule if you like the certainty of knowing your repayments are fixed, then fix. Otherwise variable is better be causing you are not paying for the additional benefit of knowing you have a fixed repayment amount.
At present B of I seem to be deliberately over pricing their variable rate in comparison with their fixed rate, so that a fixed rate may be worth considering there, but not please because you think that you are cleverer than the banks and can spot a misplacing opportunity.