interest lost because of transfer delays

No it isn't.

No, it's actually twice as bad.

Each pound you deposit and later withdraw loses 3 days on the way in and three days on the way out. Each such pound withdrawn monthly would have spent on average half a month earning interest between the moments of transfer-in and transfer-out if these transfers had been instantaneous. That's 15.2 days. But if every pound loses 6 days, then the average pound only earns for 9.2 days and this means that you lose almost 40% of the interest.

But this is a worst case result which applies only if the account is completely zeroed out each month. If any money stays in there long term, the effective interest rate won't be quite so low.

Any money you cycle yearly would have spent an average 182.5 days earning without delays and 176.5 days with delays, so the delay would only lose you some 3.3% of the interest.

If your two banks have branches you can visit, you can avoid the 3 day delays by withdrawing and depositing the money in cash over the counter.

One solution to your concern is to open a current account and a savings account in the same institution which allows instant online transfers between accounts.

Yes you are absolutely right. These activities just make us frustrated. i have also gone through such experiences.