Do you know the maximum size of a trailer (including caravans) that may legally be towed by cars?

What relevance has this to tax?

Answer: 2.55 metres, with effect from 20 April 2010.

All caravans less than 2.55 metres wide (and less than 7 metres long) will be subject to VAT at the standard rate - currently 17.5 per cent.

From 20 April 2010, VAT zero-rating will cease to apply to the sale of second hand caravans that are 2.55 metres wide or less and that were originally supplied zero-rated. 

Following infraction proceedings by the European Commission, the UK now needs to permit the same width trailers (including caravans) to be towed by cars on the public highway as in other parts of Europe. The Department of Transport are therefore amending Regulation 8 of the Road Vehicles (Construction and Use) Regulations 1986 to increase the maximum trailer width from 2.3 metres to 2.55 metres with effect from 20 April 2010. 

Since the zero rate for caravans is directly linked to the Road Vehicles (Construction and Use) Regulations 1986, any increase in the size of trailers (including. caravans) has an automatic corresponding impact on the zero rate for caravans.

We say...
very bad news for some second hand caravan retailers, good news mainly for boat owners, for example a Hobie Cat 16 catamaran is 2.41 meters wide: you can now tow legally.

Source: Revenue and Customs Brief 20/10