The truth is no one knows. All they and we can do is guess.
As the BoE base rate is 0.5%, which is different to the 3% you are being offered, how will we know what the banks will do when the rates increase. There are very few people with an idea, and these are going to be strategists within the banks product teams deciding what they need to do to attract or retain customers, and with influence on the desire to capture more capital through savings, this may or may not increase the savings rates.
If you have money to save now, I'd reccomend finding the best deal you can, and bet on this (as a certainty) rather than waiting to see if it will improve, and lose any over the top interest that could be receiving in the meantime.
You should also make sure you are making the most of your ISA capacity as this does not deduct tax from your savings unlike other accounts, so you need to take this into consideration when comparing.
HTH
Sparky