Thank you Leadsled,
In the discussions on TS in the vicinity, again the last time I looked, as the forecast applies to a 5nm radiius, vicinity was defined in the ICAO books 5 to 10 miles, so legally TS in the vicinity (between 5 and 10 miles) does not mean an alternate must be carried.
If anyone wants to look it up, refer to
Jepp Ref Met 8.1
AIP Ref GEN 3.5 Para 3.4.1.
I can't believe it took over 70 responses for someone to answer the original question correctly from a legal perspective. Apologies to anyone in the middle that I might have missed - I gave up reading and skipped to the end in disgust.