I was considering swapping my tyres front to rear so all 4 need to be replaced at the same time, but how will I know when to change them around?  I have had my Fiesta 18 months and the mileage is nearly 11K. All the tyres are wearing fairly evenly; the fronts are down to 5mm and the rears 6mm. I have Premium Contact 2 all round, what sort of mileage can you get from these. I will probably change the car at 3 to 4 years old with 25k on the clock, could I make these tyres last to then?

I did this on my Mk1 Focus.

We only do low mileage, 5 to 6k and in 10 years only used 2 sets of tyres. 1 set didn't wear down the tread but the walls started to go!

Has it been main dealer serviced?

Sounds like they've rotated the tyres previously if so, usually fronts wear out far quicker and rears barely at all.  

I swapped my fronts to the back after about 15k as the shoulders had worn to thier limit (little triangle on sidewall) from corners and roundabouts and were getting slippy at wet corner pull outs.  Rear shoulders never wear so theyll be fine on the back.  

On my 2007 Fiesta I did about 16,500 miles per year and totalled about 145k miles before selling it. The front tyres lasted about 25k, the rears about 50k. That meant that the optimum time to swap front with rear was about 18,750 miles (which is half way between half of 25k and half of 50k). Tyres were 195/50/15. Obviously driving style affects it. Mine was motorway for about 75% of mileage and I drive in a moderate way, not like a boy racer but not like an old lady.

If you look in the manual it suggests swapping them around every 4-5k, this is so the difference in wear is as small as possible, it's not a good idea to have the tyres with the most wear at the back.

OP you might get 25k out of a set but most buyers etc would notice and may knock money off for replacements, also how worn do you let them get? Legally 1.6mm is ok but they are past their best grip wise at 3mm. These 4 bits of rubber are what keeps you on the road but people don't like to spend money on them.