@ErrolTheDragon
Not sure it's been mentioned, but one detail to be aware of with PBs is that their numbers don't go into the prize draw instantly. So you don't want to be taking money in and out of them on very short timescales eg just a few months. That would reduce your odds a bit.
Good point, that's something I always forget.
Fewer than 5% of people pay tax on interest anyway. Because the personal savings allowance lets most people earn up to £1,000 in interest without paying tax on it
It's probably quite a bit less than 5% considering that the most interest you could get would be about 1%, which would mean that you'd need to have over £100k in cash savings to exceed the PSA. Or if the OP is a higher rate taxpayer, the PSA is £500 so would adjust accordingly.
So kind of makes cash ISAs almost redundant, especially as for a long time, the interest rate has been lower than standard instant access accounts, although this might be changing a little now.
OP another option would be to look at short term fixed rate accounts, because you can get around 1.1% interest.
With PBs, you're basically gambling this guaranteed interest. You might get a better payout, you might not. Depending on how much savings you have, you could split between PBs and the best savings account you could find, bearing in mind you've a lot better chance of getting close to the average 1% PB payout the more you have, eg more than around £10-20k. Below that, probably just stick with a savings account.