Over the years I have encountered a number of locator systems:

Latitude and longitude

GB national grid references

QRA locator

QTH locator

Georef

Maidenhead

I am planning some HF propagation experiments from underground and need to know 
which locator I should be using for indicating my location in the UK.  If the 
answer is not NGR I would want to feed the latter into a computer program.

Suggestions, please?

Regards,
John Rabson G3PAI