Mystery freight train-Willesden
 

I was travelling from London Euston to Harrow this afternnon on the WCML and as I passed sidings near Willesden I caught a fleeting sight of a very unusual freight train. I think it was either Class 47 or 56 and it wasn't just a heritage affair- it had a long train of hoppers behind it. The livery was also unusual- dark green and quite clean. Does anyone know what this was?