Slight timing chain rattle at 2500 rpm then goes at about 3000 rpm. Anything to worry about? If so, how much should I expect to pay for new tensioners to be fitted in the uk? Thanks!

 

Please tell us the year model of your car.

Basically there are three tensioner designs: Plastic, plastic with spring assist, and metal. Plastic goes to 01/02, spring assist 02, and metal 03 and up. You have to pull a cam cover to see what you have.

Yes, it is something to worry about. If the secondary chains skip more than a couple of teeth, it will destroy your engine.

Do not start or drive the car until you have it repaired.

Secondary tensioners over here are a $200 DIY, $800 Indy, and $1600 dealer job, not sure about the UK.
Vector

 

I had mine done a couple of months ago latest tentioners water pump while in there and thermerstat by my local jag specialist £730 with the VAT worth every penny

 

blue:
It won't take much searching in the archives to understand that, YES, there is extreme cause to worry, unless you have a spare engine nearby!
Jumped chains on this car result in valves crashing the pistons, and that means big trouble!

 

Although timing chain tensioners are a major worry, they usually rattle at startup and the noise goes away at higher RPMs. What year is your car ? In any event, it wouldn't hurt to pull the cam covers and have a good look.