After WWI the British government promulgated the "Ten Year Rule" which declared, rather optimistically, that there would be no major war involving Britain for at least ten years and therefore defence spending could be cut. (This was predicated on the losses taken in WWI and a wish to not repeat them).
Unfortunately the rule was interpreted as starting from this year, i.e. whatever year it happened to be when defence spending was being discussed.
It wasn't officially repudiated until October 1933. Although the government, being the government, did manage to stint on defence spending for a bit longer.
Basically the unpreparedness arose from a mixture of Horror over the casualties of WWI, a reluctance to go through them again, and wishful thinking.
Fortunately Britain was such a powerful nation in terms of capacity that redressing the balance didn't take long. This was helped by the fact that the German economy and manufacturing industry didn't go onto a war footing until late 1943.
1939
In 1939
1939
In 1939. 1914 to 1918 and again from 1939 to 1945
september 1939
Britain and France declared war on Germany on September 3rd 1939, two days after Germany invaded Poland.
Great Britain declared war on Germany in September 1939 after Germany invaded Poland.
Great Britain and France declared war on Germany in 1939, because germany had invaded land that Great britain had to protect for france.
Although Militarily unprepared, Britain declared war on Germany, September 3rd 1939 after Hitler invaded Poland. Hitler had previously broken a peace agreement not to invade Czechoslovakia.
Because of Germany's attack on Poland.
The 1939 invasion of Poland caused Britain to declare war on Germany, which started WWII.
On 1st September 1939, German troops invaded Poland. In response to that invasion, Britain and France declared war on Germany on 3rd September 1939.