Switzerland is your country of issue because they issued your PPL.
But don’t confuse the rules for transferring a license and issuing a new license. Any ICAO PPL (+ the other requirements) is sufficient for CPL training and subsequent issue of the JAA license by the UK CAA. After they have issued your new license the UK will be your new country of issue. You do not have to be a resident in the UK.
Ones you return to Switzerland – because of your residency – you have the right to change your country of issue, which will the terminate your PPL (you don’t need it anymore).
Or you can’t just hand the PPL back to the Swiss authorities and keep the UK as the country of issue.
I personally did my ATPL, CPL and ME/IR training in the UK on my Danish PPL, got a UK CPL license from CAA (they express mailed it to my Danish address) and then handed in my PPL to the Danish authorities.
In fact I tried to transfer my PPL from Denmark to the UK, but was told by the CAA that it was unnecessary.
The Viking