Fighting the fat can be a difficult issue - and not just for our waistlines. Old cooking oil from our takeaways and roast dinners can cause major problems - from polluting watercourses to blocking sewers and causing flooding if not disposed of carefully. But rising commodity prices and surprising new uses have turned it from waste product to wonder in some people's eyes.

Tom Heap slides his way to a fat recycling plant where everything from large scale tubs of mayonnaise to tiny butter sachets and even pork scratchings are seen as a golden resource which can be treated and turned into fuels. Out of date or overcooked foods can still find a purpose - even 'frier sludges' are valued here.

So how far would Tom go in pursuit of useful waste fat? A trip beneath the streets of London to the sewers sees him in search of 'fatbergs' - created by the build up of grease thrown down our sinks. Some as large as double-decker buses have been found which have to be blasted out to ensure they don't block the system and cause sewage to flood people's homes. Now instead of being sent to landfill they're being put to good use - despite being once of the most degraded fats on the spectrum.

Meanwhile the University of Wolverhampton has been using oil from the local chippy and canteen for its lab experiments. They've been able to make a bioplastic - something so pure from something so dirty - that it will be used inside the human body to aid healing.

Produced in Bristol by Anne-Marie Bullock.