I read this in the FT, on the subject ..

Pension tension

The end of passporting arrangements could also prevent private pension companies in the UK from paying pensions to millions of retired expats living in the EU, according to the Association of British Insurers.
“A no-deal situation would leave insurance contracts in a legal limbo, where insurers would be unclear if they could legally pay claims for contracts that have been written pre-Brexit, which would have to be paid out in countries in the European Union,” says Huw Evans, director-general of the ABI, which is calling for the issue to be urgently addressed.
Speaking at a hearing of the Exiting the European Union committee, Mr Evans said there was a “perfectly plausible” risk that some British pensioners living in EU countries post-Brexit might not receive their pensions, if the issue was not resolved.
Experts have identified an expensive though long-winded solution. Life companies could, in theory, set up an EU subsidiary, and transfer the pension policies there to be paid out from an EU entity. Some firms are already doing this, but others are waiting to see if any other form of solution can be brokered.
There is also uncertainty over state pension arrangements for expats post Brexit. Currently, the UK state pension is payable overseas but annual inflation rises are only applied to the pension if the pensioner is in an EEA country or one with which the UK has a reciprocal agreement requiring uprating.
The rules post-Brexit will depend on the outcome of negotiations. However, the government’s July 2018 white paper said the UK would seek reciprocal arrangements, which “could cover provisions for the uprating of state pensions”.