Oh dear Day6 - I started to read Tim Loghton's letter you posted and thought it sounded like a reasonable explanation, though I expect the "acquired rights" he mentions in relation to property may vary country by country.
However, towards the end he makes this rather telling point:
In terms of people's working rights, this is one of many things that will need to be negotiated after we come out of the EU.
This could be interpreted to suggest major back-pedalling on the Working Time Directive, and other in-work, and social issues. Maybe the "British Bill of Rights" proposed by some could offer more 'flexibility' still with imposed, iniquitous 'zero hours contract' terms.
I'm not saying that the EU approach resolves or is likely to resolve these issues, but given their reputation over the past decade or so, I don't think our parliament has either the willingness or integrity to address those potential pitfalls.