  We present observations and analysis of a sample of 123 galaxy clusters from
the 2013 Planck catalogue of Sunyaev-Zel'dovich sources with the Arcminute
Microkelvin Imager (AMI), a ground-based radio interferometer. AMI provides an
independent measurement with higher angular resolution, 3 arcmin compared to
the Planck beams of 5-10 arcmin. The AMI observations thus provide validation
of the cluster detections, improved positional estimates, and a consistency
check on the fitted 'size' ($\theta_{s}$) and 'flux' ($Y_{\rm tot}$) parameters
in the Generalised Navarro, Frenk and White (GNFW) model. We detect 99 of the
clusters. We use the AMI positional estimates to check the positional estimates
and error-bars produced by the Planck algorithms PowellSnakes and MMF3. We find
that $Y_{\rm tot}$ values as measured by AMI are biased downwards with respect
to the Planck constraints, especially for high Planck-SNR clusters. We perform
simulations to show that this can be explained by deviation from the
'universal' pressure profile shape used to model the clusters. We show that AMI
data can constrain the $\alpha$ and $\beta$ parameters describing the shape of
the profile in the GNFW model for individual clusters provided careful
attention is paid to the degeneracies between parameters, but one requires
information on a wider range of angular scales than are present in AMI data
alone to correctly constrain all parameters simultaneously.
