I have told a friend of mine that Muslims can drink alchol, but not if
it is made from grapes (as well as other things). For example I
believe the Koran allows the prudent imbibing of honey based alcohol.

Question:
Is it true of false - The Koran prohibits the consumption of grape based alcohol?

Dear Kongulu, 

Let's begin with the fact, that religion, or holy scripts, could be
interpreted in man ways. Saying that your friend is right, wouldn't
mean that you are not: different people interpret their religion
differently, and therefore also act differently. Therefore, different
people would also give a different answer here.

Basically, all alcohol consumption is prohibited. The reference is to
"strong drinks" in general, not only to grapes, but also (for example)
to wine produced from dates. See for example:
Nathan Laing, "Intoxicants Strictly Prohibited", Submission
<http://www.submission.org/drugs/alchohol.html>

However, you can find some Muslims who consume alcohol for "medicinal"
purposes. The site "Andelusian Wines", for example, tells us that
"Wine was appreciated even during the centuries of Moorish domination:
the Koran frowns on the consumption of alcohol, but the Moors made
wine and imbibed it with gusto, for "medicinal" purposes. They even
introduced the technique of distilling into Spain. The Spanish word
for still, alambique, is Arabic in origin, as is the English and
Spanish word, "alcohol"." (SOURCE: Andelusian Wines,
<http://www.andalucia.com/gastronomy/andalucianwines.htm>).

Wine taverns and wine poetry were also common, despite the
prohibition. Christine Schirrmacher writes in her article on alcohol
prohibition, that despite the unambiguous condemnation, people
continued to consume alcohol.
(SOURCE: Christine Schirrmacher, "The Islamic Faith and the
Prohibition of Alcohol", Institute for Islamic Studies,
<http://www.islaminstitut.de/english/publications/alcohol.htm>).

I hope this answered your question. If you need a clarification on
this answer, please contact me before you rate it.

The information provided in the two answers was enlightening and has
provided background for furhter research. Thank you.

A long time ago a pretty well educated Muslim told me that alcohol was
not forbidden in the Koran, but it was forbidden to enter a Mosque
while intoxicated.

This was when I queried whether he should be imbibing a rather hefty G&T.

The Sufis, who follow the Koran, are pretty keen on 'wine' - which I
understand is also a euphemism for wisdom.

In practise, standing in the alleys outside the Mosques above the
Wailing Wall, on a Friday afternoon, the smell of hashish coming from
the streaming hordes of the faithful is ... quite interesting. Even
more interesting, that the partakers are pretty elderly.

PoliticalGuru's first link to Nathan Laing's page looks pretty conclusive, 

"O you who believe, intoxicants, and gambling, and the altars of
idols, and the games of chance are abominations of the devil; you
shall avoid them, that you may succeed." 5:90

However, these ancient self help manuals tend to be riddled with contradictions.

I wonder whether there is an online/downloadable Koran somewhere on the web ....

Thasnk you for the rating and the tip!