First, the amazon blurb from David Hurwitz claiming that Ireland's piano concerto is "more or less the English equivalent to Prokofiev's Third, and if you enjoy that work, or Gershwin, you'll want to hear this one" reflects a lack of insight into Ireland's music. Ireland was gloriously mysterious, not "jazzy," whereas Prokofiev was frenetic and dissonant. As much as I like Gershwin - and I assume Hurwitz had his Concerto in mind - I would never connect him with Ireland either. Ireland's concerto is English "modern" and while the composer may have been influenced by Prokofiev's Third, which premiered nine years before Ireland's concerto, it's not in any way "equivalent."
Anyway, Eric Parkin is the foremost champion of Ireland's output for piano, so it almost goes without saying that these are authoritative performances. The only issue is that Parkin's earlier recordings with Adrian Boult of both the piano concerto and "Legend" for piano and orchestra are better (Boult conducts John Ireland). Parkin and Boult deliver marginally tighter readings than Parkin/Thomson who tend towards slightly romanticized phrasing here and there. On the other hand, if you want "Mai Dun," another Ireland essential which appears on this disc, then you'll have to get Boult Conducts Ireland. Both Boult/Ireland discs are wonderful, and the mid-1960's sound is fine (Lyrita was known for their exceptional sonics).
If you want Mai Dun, Legend and the Concerto, which are hang together very well, and want only one Ireland disc, then you'll be fine going with Parkin/Thomson. Otherwise, I would recommend buying both of the Boult discs on Lyrita.