how many UK businesses have websites?

Dear scaredycat-ga,
There is no definitive answer to this question. First it depends as to
what you mean by businesses as this can included limited liability
companies as well as partnership and sole traders. Only the former has
to register with Companies House. Then there is no cross reference to
domain name registration either at the .com level or the .co.uk level.

The most reliable statistics are from a UK government survey conducted
in 2003 (and previous years). They sent a survey to a sample of 12,000
UK businesses across a broad spectrum of size and activities - 84%
answered. From the data supplied they have estimated figures for the
UK as a whole. The survey also contains a considerable amount of
information on other aspect of the use of the internet by businesses.

"Websites have become an essential part of many businesses'
communication with their customers; although possibly not for sales.
At the end of 2003 the number of businesses that reported having a
website rose to 31 per cent, up 7 per cent from the 2002 figure of 29
per cent and from 25 per cent in 2001. The largest businesses (1000+
employment) are nearly four times more likely to have a website than
the smallest (under 10 employment). More than 8 in 10 businesses with
more than 50 employment had a website at the end of 2003 (see Table
4).

More businesses in the Banking, Financial and Insurance Services
sector have websites than those in any other sector, 46 per cent at
the end of 2003, while only 26 per cent of manufacturers reported
having a website, the lowest sectoral group. Interestingly, a high
proportion of websites do not allow visitors to buy on-line."
Page 3 (see also Table 4)
http://www.statistics.gov.uk/downloads/theme_economy/ecommerce_Nov2004.pdf

Links to previous years'data
http://www.statistics.gov.uk/about/Methodology_by_theme/e-commerce_related_activities/default.asp

Apart from the above, during my research I found widely differing
several estimates but the methodology was not stated. I therefore
consider the UK survey to be the most reliable.

I hope this answers your question. If it does not, or the answer is
unclear, then please ask for clarification of this research before
rating the answer. I shall respond to the clarification request as
soon as I receive it.
Thank you
answerfinder

Search strategy
Knew of UK Government statistics site, also searched DTI.
uk businesses "have websites"
://www.google.com/search?hl=en&lr=&q=uk+businesses+%22have+websites%22&btnG=Search
uk businesses "have web sites"
://www.google.com/search?hl=en&lr=&q=uk+businesses+%22have+web+sites%22&btnG=Search

Excellent. Exactly what I was looking for.