Hello Guys,
Following some great advice from Doc, I bought a VW sat nav off eBay for £450 which was nearly new. The antenna was placed on the dashboard next to the door pillar. The next purchase was a navigation disc which cost £80. Total cost including fitting £640

Works perfectly and used it to travel from London to Poznan, Poland. Did not miss a beat

An interesting feature was that the unit showed all traffic and roadworks on route and tried its best to avoid them. Something the UK does not transmit via radio!? I had a portable unit before but nothing compares to this. It looks pukka and works extremly well