Two passports: helpful - or not?

[BaiLao]

A friend has two valid passports, both from Commonwealth countries. In theory, could the person use these, alternating between the two for a year, on SETVs from neighboring countries? For example passport 'A' could be used twice (60 days plus extension) and passport 'B' used the same way, giving an effective total of nearly a year. What evidence is there to suggest that, at some point, the two passports would be linked and questions asked at DM or S? 

[ubonjoe]

If the passports have the same name and date of birth on them they will be linked the first time the other passport is used for entry.

[elviajero]

Having two passports would help in getting visas as the embassies/consulates only seem to count the visas in the passport being used when deciding whether or not to issue a visa.

 

But the immigration system will identify a possible link as soon as you use the second passport. Once the IO confirms the link your entry history from both passports will be used by the IO’s when deciding whether or not to let you enter.