Just a quick update for those in the same boat. DAN, my insurer, are happy to insure me to dive with a PFO and ASD, even if I don't have closure. I suppose they reason that I'll go easier as I know about it more than someone who doesn't - quite refreshing from an insurance company.
The doctor who does my HSE medical is also happy to let me dive but with limits. No deco, no trimix, max 30 metre, must dive on nitrox with computer on air mode and stay well away from deco limits, slow ascents, avoid CESAs with students etc etc.
I've decided I want to do whatever I want to do so I'm going for closure in December. If all goes well I can get back to whatever diving I want to do. If not then we'll have to wait and see. Perhaps knitting or bowls
Paul.