That was Sir Neville Chamberlain.
Neville Chamberlain
British minister who, along with French primier Edouard Daladier, practiced a policy of appeasement toward Hitler
Nevil Chamberlain is well known for a public policy of appeasement.
Good or bad didn't matter, appeasement failed to prevent Hitler's ambitions.
When Hitler invaded Poland.
The name of the agreement referred to in the question was the Munich Agreement. The term used to describe the policy and/or philosophy behind it was appeasement.
Britain exercised a policy of appeasement with Hitler because initially, his demands were reasonable. The belief was that if appeasement was used, he would eventually become satisfied and stop his aggression. The British Prime Minister, Neville Chamberlain believed that appeasement was the appropriate tactic.
Prime Minister Neville Chamberlain foolishly believed that Adolf Hitler would leave Britain alone if they signed a non-aggression pact. He was trying to save British lives. The French thought the same thing. Hitler's Anschluß referendum showed Hitler that Brits and French were "wimps" trying to appease Hitler. This was to the demise of the Brits and French after they signed the phony appeasement documents.
Poland
invaded Poland.
Appeasement will forever be associated with British Conservative Prime Minister Neville Chamberlain. In signing the Munich aggreement he appeals to Hitlers 'better nature'. Put simply Hitler didn't have a better nature. Appeasement is a vain attempt to avoid a repitition of WW1 in Europe.
Neville Chamberlaine