Is a British subject, travelling to the USA, required to show that he has, on his person, the sum of $1500?

You are required to to tell the inspecting officer how much currency and monetary instruments you are traveling with, or someone else who may be holding money for you. Monetary instruments is cash of any kind, Dollar, Pound, Euro etc etc.., coins, travelers checks, and endorsed checks and money orders made out to you. You are required to formally declare $10,000 or more of currency or monetary instruments or a combination of the two equaling $10,000 or greater.

Google "CBP Know Before You Go" if you have anymore questions.

**Kittysue, I don't know about these scams your talking about, but if a CBP Officer asks you how much money you are traveling with, you better answer, or you're not coming in. If he asks you to verify the money you declared and you don't, you're not coming in. If you declare $1500 and the officer verifies it to be $6500 then that money gets seized. And if someone shows up to be inspected with $1 and no other money or credit cards, they're not coming in. I would know, because I am a CBP Officer.

Is your brother still here? HAHA

No, you are not required to have any specific amount of money to travel to the US and nobody ever asks. On US customs forms you have to declare ONLY if you are carrying more than $10,000 in cash with you. Otherwise there is no minimum requirement

You could travel to the US on the visa waiver even if you had only $1.

Anyone saying they need money to show to travel to the US is scamming you. The American Embassy in London even has a warning about this on their website as it is a common scam to get you to send money to criminals. They will keep coming up with more and more excuses why they need money until you stop sending it to them
http://www.usembassy.org.uk/americanservices/?p=691
http://london.usembassy.gov/cons_new/acs/scs/internet_scams.html

"Beware of anyone who requests funds for a BTA, or Basic Travel Allowance, as a requirement to depart another country for the United States. There is no such thing as a BTA. In other cases, your Internet friend will claim to need a travel allowance, or travel money, to be able to travel to the United States. Again, there is no such requirement under U.S. law. "

Cut off all communication with this scammer and report them to the FBI. If they are scamming you they are also trying to pull the same scam on hundreds of other people they met online

My brother came in with 50p and they let him in. He just said that he was going to be staying with relatives and gave an address. It was a fine moment in his life.

And the answer to your question is no, you don't have to show a particular sum but you do need to show that you have enough funds available for the trip you are planning. Visit relatives and you will need enough for the phone call if they don't find you at the airport. Visit five cities and you need to be able to tell them how this is being funded if they ask (they don't usually).