The BBC had little or no hand in "designing" PAL.
The original NTSC proposal /was/ PAL. Want proof?

So the PAL patent is owned by a US company?

You mean "was". And there would have been multiple patents.

The PAL system was publically described in an "Electronics" article circa
1951, which I have in the garage. It was given as the NTSC proposal. It used
phase alternation, and equal-bandwidth R-Yand B-Y primaries.

It was presumably patented, so I assume someone would have had to pay
royalties at least through the mid-60s.

I well-remember reading -- many years ago -- that European TV-distribution
systems suffered from significant non-linear phase errors (while American
systems did not), and this was the principal reason for adopting phase
alternation. I have no source, though.