Blocked payment by the bank

[beetlebugslife]

We’re hoping for some advice.
My elderly dad needs some building work carried out on his property. Although my siblings and I live some distance away, we’ve managed to arrange several quotes and, between us and Dad, we’ve chosen a builder to go ahead with.
The builder has requested a deposit, which seems perfectly normal. However, Dad banks with NatWest and the builder uses an ANNA business account. NatWest’s fraud team have repeatedly blocked the transfer, saying they believe it’s potentially fraudulent.
We’ve done as many checks as we can. We’ve looked at TrustATrader, Google and Facebook reviews and haven’t found anything concerning. The business doesn’t appear on Companies House, but we appreciate they may simply be a sole trader, so that in itself isn’t necessarily a red flag.
Following NatWest’s suggestion, we asked whether the builder could take payment by credit card or PayPal, but they don’t offer either. We also tried sending the payment from a Halifax account instead, but that transfer was blocked too. Both banks have said the business isn't registered, which seems to be what's triggering the fraud alerts.
We're keen to pay in a way that protects Dad and provides a clear payment trail, so we'd rather avoid paying cash unless there's no alternative.
A quick Google search suggests that some high street banks can be cautious about payments to ANNA accounts because of the way their fraud detection systems work, although I don't really understand the technical side of it.
Has anyone experienced something similar? If so, how did you manage to make the payment, or is there another secure method we should consider? Any advice would be greatly appreciated.

Most builders or trades would rather the customer bought the materials themselves as they are taxed on all income as well as having vat implications.

No they’re not. They’re taxed on profits.

There are only VAT implications if they are not already VAT registered, otherwise they charge VAT on the goods but reclaim the VAT they pay on the goods.

Weird thread.

Of course deposits are not unusual. I have a construction company. No way am I booking a job/ ordering/ mobilising without deposit. Been burned way too many times.

Also pay deposits to other workmen regularly. Obviously depends on the scale of the job whether that is necessary.

I have had this once before. Bank wanted to block and I just went mental at them and they let it through. Tbh main banks are a nightmare for blocking not just transfers but online payments and it’s part of why I have moved my current account to monzo.

Never heard of Anna so can’t comment on that. Nor whether this builder is legit.

But lots of traders do use fin tech challenger banks. We do ourselves because the big banks have horrible user interfaces / apps, poor accounting tools and high monthly fees.

Thanks for everyone input

This afternoon my dad transferred the money to my sister and she made the payment. We now think it’s possible my dads account has a red flag

A lot of the banks are putting in extra checks when over 65's transfer large amounts of money to new payees.
Recently a friend had to go through a quite intensive security check before he could transfer money into a different bank account via his banking app because this was unusual activity for him.
It was annoying at the time, but at least the banks were trying to protect him. Did your father not get a message on his app explaining why the transfer was blocked and what to do next?