Old Grey Wolf, your request take me back to days long before the Blitherscrum Festival to that amazing summer of 68 (or was it 67?) when Old Farmer Jones's son, Speedy George, established a sort of commune out on Eel Pie Island in the River Blither and he used to sing this song late at night.

When the weather is fine come and have a good time,
Messing about on the Blither;
For all kinds of vice, there is nothing so nice,
As messing about on the Blither.
Losers and users with all kinds of dope,
Cruise with a nice girl who'll tie you with rope,
So take off your kit, turn on for a bit,
Come messing about on the Blither.

Lebanon Red that will leave you half dead,
When you're messing about on the Blither;
Acid for trips with hip cats on the ships,
While messing about on the Blither.
Potions and lotions and all sorts of pills,
Leave you reeling and feeling green in the gills,
So lie down on your back,be free with the smack,
When you're messing about on the Blither.

Stardust and golden, Aquarian children,
Messing about on the Blither;
Generation of love we will not move,
From messing about on the Blither.
Onwards and upwards we'll sail to the stars,
Calling at all ports to Venus and Mars,
The universe calls, break down the walls,
By messing about on the Blither.

Drop out of school, come and be cool,
Come messing about on the Blither;
You're never square with flowers in your hair,
When you're messing about on the Blither.
Guitars are strumming, bongoes are drummming,
You can hear the air filled with musical hummimg,
Float along in your boat while you take a tote,
Just messing about on the Blither.

Or perhaps you were thinking of this song? Messing About on the River/Tony Hatch

I wonder what happened to Speedy George? He was in the original line-up of the prog rock band The Lovebites but disappeared in Morocco before they cut their seminal first LP 'The Flight of the Fairy Fortune Teller'.