In 2001, the UK Hydrographic Office (UKHO) claimed copyright over all the existing tidal data that they maintained, covering the UK as well as some countries outside the UK. They removed the information from the public domain and started to charge to use it.
Unfortunately it appears that there wasn't anybody with sufficient resources to make an effective challenge via the courts. So for a while there was no freely available UK tidal information.
However, at the end of 2003 the British Oceanographic Data Centre agreed for its own data (collected independently from the UKHO) to be used in XTide which is the "engine" that drives many of the free tide prediction programs. This means that certain key UK ports are now available in programs like WXtide32.
More details about UKHO's action here: http://www.flaterco.com/xtide/faq.html#60
More details about the new UK tidal information here: http://flaterco.com/pol.html