Some bigger Bangkok Bank branch offices allow to withdraw money over the counter. This will evade the typical 220 baht ATM fee, but will take some time and passport is necessary. Exchange rate is always determined by the card issuer (usually Visa or MC) unless local bank currency conversion is opted which no one should ever fall into.
Withdraw money directly from the bank counter as a cash advance, at least Bangkok Bank does that without any of their own fees. May take some time depending of the branch due to various red tape (PP required) but with a travellers bank card such as Revolut or Wise the home bank fees are negligible.
It was actually my friend who got caught (despite all the precautions) and were offered the special deal. I think it was 500b at the time and saving 300b buys you several pad kra pao’s.
It has been discussed many times over and over again in various internet forums. Primary sources are 1979 Thai Motor Vehicle Act, sections 42 and 42.2, and the previously mentioned conventions, all very easy to find with Google.
However, that said, if you want to avoid troubles with bent or simply ignorant police officers and possible insurance issues, by all means it’s much easier to go with the IDP or get a Thai drivers licence even when you would not be legally required to have one.
“You must always have your IDP along with your national license at all times”. That’s just simply wrong, since the 1949 Geneva Convention many nations have adopted mutual acceptance of national drivers licences.
According to the Thai traffic laws yes you can. However, the police may not share the view as there has been some areas open for interpretation regarding the international road traffic treaties Thailand have ratified.
Since May 2020 Thailand has ratified the 1968 Vienna Convention on Road Traffic. If your national driving licence has been issued in a country which is a party to that treaty, like most of the countries are (UK included), there's really nothing unclear and your national driving licence should be valid in Thailand as long as it is used for tourism (international travel) purposes. However, for those countries which are not parties of the Vienna Convention the question remains somewhat unclear because the preceding 1949 Geneva Convention (to only which e.g. US and AUS are parties of) was meant to be replaced by the Vienna Convention and has technically obsolete definition of the form of the accepted national driving licence.