  We have used new parallax measurements, obtained by the Hipparcos satellite,
of fifteen nearby, metal-poor stars to re-define the subdwarf main-sequence.
All of these stars have parallaxes determined to an accuracy of at least 12 %.
Comparing these measurements against previous ground-based data for nine stars
reveals a systematic offset of 5 %, in the sense that the Hipparcos parallaxes
are smaller (i.e. the inferred distances are larger). The availability of the
Hipparcos observations expands the local subdwarf sample to the extent that we
can separate the stars by abundance into intermediate ([Fe/H] ~ -1.4) and
extreme ([Fe/H] ~ -2) subsets. Main-sequence fitting techniques are then used
to match stars of the appropriate abundance range to the colour-magnitude
diagrams of the seven globular clusters M5, NGC 6752, M13, M15, M92, M30 and
M68. We derive respective distance moduli of 14.45, 13.17, 14.48, 15.38, 14.93,
14.95 and 15.29 magnitudes, with formal uncertainties of +/- 0.1 magnitude. The
metal-poor systems M68, M15 and M30 have moderate foreground reddening, and
varying E(B-V) by +/- 0.02 magnitudes can change the derived distances by up to
+/- 7 %. With the exception of NGC 6752, however, our derived distances exceed
previous estimates, particularly in the case of the four [Fe/H] ~ -2.1
globulars, where our distance moduli are ~ 0.3 magnitudes higher than the
current standard values. We discuss briefly how these findings affect the RR
Lyrae distance scale, isochrone-based estimates of the age of globular clusters
and our picture of the early stages of star formation in the Galaxy. We note
that our results go some way towards reconciling the apparent contradiction
between the cluster ages and recent determinations of the Hubble constant.
