Where British sold out Poland to the Soviets in Potsdam, and Yalta conference.
I'd say moreso the sell-out manifested in real terms at Teheran. I've detailed my position there elsewhere on the forum if you are interested, but briefly, HMG sold Poland out to the Soviets by acquiescing to Stalin's designs on Polish territory. Otherwise, HMG also breached Article 5 of the Treaty of Mutual Assistance by virtue of failing to tell Poland of the fact that they had done so, and, more pertinently, by failing to tell Poland of Stalin's designs.
I think Molotov illustrated the perfidy best when he expressed to a stunned Mikolajczyk during discussion on Polish territories that no, Poland couldn't have Lwow and Vilno back because "all had been settled at Teheran".
Where British went against Polish marching in victory parades.
Sad, isn't it.
To be fair though, certain very small elements of the Free Polish air force were invited, as well as a couple of senior officers (I think Bor was one). All eleventh hour invites mind you (something like the night before the parade), occasioned by virtue of the "Communist Polish" forces scoffing at their invitation.
Snubbed, HMG must have realised that with the absence of their new Communist friends attending, their erstwhile Free Polish friends would be slightly better than nothing. As befits such contemptible "invitations", they were politely rejected.
Where British basically stole Polish gold, to pay for the Polish armies mantenance.
It wasn't "stolen" so much as held on "Trust" by HMG, who invoiced the Free Poles and deducted the Polish gold reserves held on trust in settlement of the bill.
Kind of like a situation whereby you're my friend and your house catches fire but I'm too busy to help you. But, when my house catches fire, you and your family (you're lodging with me now (but not your family) and I hold your stuff on your behalf) rush to help me put out the blaze, and, in gratitude, I take some of your stuff that I hold in payment for the hose you used and the extra water you consumed in putting out the fire to my house. Good, isn't it?
Why does Poland need enemies, when it has such lousy friends as Britain?
Again, in fairness, this all happened a long time ago, and should not be the sole benchmark to which modern-day Poland gauges its relationships with foreign countries. It's not "the Brits" who did this, but rather their Government at the time. I'm sure that if the average Pom had known about the absolutely atrocious way in which HMG treated the Poles, they would have been up in arms. Indeed, this sort of spirit of honour and fair play resonated with some MP's, who actually resigned in protest over the way Poland was treated.