Hello Stephen101,
I would think much the same as you, with regards to the likelihood that the property is crossed secured over other debts, given you've mentioned that the vendor owns a number of properties. Assuming that to be the case, there is quite possibly a change in the Bank's Loan To Value (perhaps there's negative equity, perhaps not) so it will require a Bank to make a credit decision (hence, someone has to submit a recommendation, someone else sign off on it etc.). This takes time, not least because it's not a priority within a Bank most of the time.
It's also possible that the Bank, or the solicitors who acted for the Bank and perhaps store the legal documents for the Bank, have misplaced documents. Likewise, it's possible that some work has been carried out on the title behind the sceenes (remedial work, possibly separation of a folio etc.) and needs completion, before the deeds can be released on ATR.
As for the oral consent, you'd expect a the oral confirmation to be reliable, but never say never. If it has only been given the last couple of days, hopefully you'll see written confirmation in the next week or so, but if it's a couple of weeks ago, then I'd get my solicitor back on the phone immediately.
If you can get direct contact with the vendor, no harm asking them if they know whats delaying it (they may or may not tell you, but if you mention a couple of gentle things like title work, or properties being cross secured without seeking details, they might tell you).