Do a Google search for SIT (Special Information Tones). Look at the 3 frequencies and time duration of each. All are +- 50HZtolerance so should work in UK or USA. You will find one tone frequency common to all 7 classes of SIT tones. First generation autodialing software looked for this tone only, next gen looks at all 3 to determine exact cause of non-hookup and may recycle the number for a later time if the situation fits.
You may get by using only the common tone, but when in doubt, use all 3.
Dialtone