A distant blockade would cut off a lot of materials such as nickel and chrome from Turkey, iron from Sweden during the winter when it has to pass the Skaggerak, and that sort of thing. Granted that these things too would be long term and not immediate, direct assistance.
Iron ore from Sweden could only reasonably interdicted during the winter (Nov thru Mar). At other times, shipments went via the Baltic into Lubeck. In 1939, interdicting the western route, via Narvik, was limited by Norway's neutrality. That said, Churchill did push to interdict ore shipments further south from December 1939 onwards. As you point out, this wouldn't help Poland.
I know nothing of nickel ore shipments from Turkey. Definitely would like to learn more about that. I'll do some digging and see what I can find out. That said, it still won't help Poland.
I wouldn't do that at all. My comment was more about submarines, which while being almost as dangerous will be likely more effective.
I wouldn't put battleships into the Baltic, although it was formulated as a plan in 1939 under Operation Catherine. Multiple objections, not least of which was an underestimation of the air power threat, resulted in Churchill cancelling the operation in January 1940. The idea of sending submarines into the Baltic is certainly worth more exploration, although I can't see that it was ever countenanced by London. The threat environment would be complicated given that the Baltic was essentially a boating lake for Russia and Germany in 1939.
I'll have to fetch a couple of books from home to answer this better. But the wall was still being constructed in fits and starts and the divisions defending it were not first-rate; those were busy attacking Poland.
Definitely interested in hearing what you discover.
I don't think GCCS was able to read Enigma until 1940. As for developing PRUs etc, that again does zero-point-zero assistance to the Poles in a useful time-frame. It will certainly help the British war effort later in the war. A fat lot of good that does the millions of Poles already dead by then.
Any Enigma capabilities in 1939 were probably heavily dependent on the Poles. My comment about PRU capabilities is to better ascertain the strength of German defences in the west. Having viable PR capabilities might have enabled a more accurate assessment of Germany's weakness in the west. That MIGHT have been of direct help to Poland.
To what end? Stalin didn't want an independent Poland. The Poles were surely right that if you let the camel's nose in at nightfall you wake up next to him in the morning. 45 years of post-war occupation demonstrated that. What happened was that the Germans, having resolved to attack Poland after they had digested the rump Czech state in Mar 1939. They hurried up their courting of the Soviets after receiving hints that Stalin would be amenable. Thus, by the time Drax et al set out for Moscow in Aug, they had already been passed up by events, in addition to the Polish intransigence about Soviet troops passing through. The Soviets rightly regarded the Allied mission as an attempt to save a deteriorating situation with them (the Soviets) to provide the muscle. But by the events were in train to send Ribbentrop to Moscow and with an agreement already in process of being hammered out.
In short, by the end of July 1939, there were no opportunities to miss.
I don't disagree that bringing in the USSR would likely do nothing to help Poland, indeed it might accelerate Russia's aggression against Poland. I can fully understand why Poland refused to allow Soviet troops on its territory.
Perhaps? I don't know. I would imagine that getting those divisions together and shipped would likely have taken some time. I don't see the Brits being able to intervene on land in time to save Poland at all. They were impotent that way.
I agree that the BEF deployed as rapidly as they could. As
S
Shortround6 has observed, the BEF wasn't a fully-prepared fighting force. The operational readiness wasn't as high as it should have been but, again, it would have been far worse a year earlier. Indeed, the size of the BEF would probably have been considerable smaller.
Any British impotence only came about because the Polish forces collapsed in the face of an unexpectedly rapid advance by the German army. However, the longer Poland military resistance continued, the better the chance of the Allies making real gains on the western front. Two weeks just wasn't fast enough, and the Allies couldn't possibly know they only had 2 weeks to act.
I think the smart money is on drawing the line after the reoccupation of the Ruhr, the te3aring up of Versailles, and the Anschluss on any further German shenanigans -- and presenting a strong face at Munich. That was the last chance to stop Hitler without war, and the Western Allies muffed it.
Again, that requires foreknowledge of how things would eventually play out. We've all agreed that the sell-out of Czechoslovakia was a low point. We're starting to have the rinse-repeat conversation again. It would be good to know if your blame of the western Allies is limited to Britain and France or if you are willing to extend blame to other nations that might have influenced events.
And the UK did not do that. This is a fact of history.
And you give me grief for not listening to your point of view...sheesh!

Your "fact of history" entirely depends on conflating the territorial definition of a nation with the political definition of a nation. Alas, that's not a correct alignment.
The European governments in exile during WW2 all considered themselves as independent, legal, and free governments of their respective nations. This was particularly the case for the Polish government which never surrendered either to Nazi Germany or the USSR. The Polish government in exile organized the Polish Armed Forces in the west, and coordinated the Polish Underground State and the Home Army. Same for the Free French who saw themselves as the legal government of France, as opposed either to the German-occupied zone or the Vichy territory. Even Czechoslovakia had a government in exile under former President Beneš as the legitimate government of the First Czechoslovak Republic.
For the most part, it was those governments in exile that reformed their respective nations at the end of the war. If those governments considered themselves the legal and independent manifestations of their countries, who are we to question it?
We have the same thing happening even today in Ukraine. The Ukrainian regional leaders of Russian-occupied areas continue to represent their regions as part of the political construct that is the whole of Ukraine. They are, legally, the legitimate and free local governments in contrast to the governments set up by the occupying Russians. If those Ukrainian regional governments don't legally represent those regions then, logically, the only legitimate governance comes from the Russian-formed governments.
I hope this explains the key distinction I am making, which is not represented in your assertion.