That will be the personal number. If you check out the Ukpsf website you can get a list of sites, for accredited a rough look ive made is in excess of 70 siteswell at the very least, businesses should have to join. There are around 300 fields, so 427 is a pathetic number.
Sadly you won't find all sites in the UK under the Ukpsf. No delta force sites are likely to join, they threw their teddy in the corner years ago and made the UKPBA