Pear rust is comparatively new in the UK - usually presents as one or two quite large bright orange spots on the top of the leaf, with a corresponding area beneath which sticks out. The bit that sticks out beneath is full of spores waiting to be dispersed, so remove and burn infected leaves - this is caused by a gymnosporangium fungal infection, also known as European Rust. Spraying thoroughly with Westland Plant Rescue Fungus Fighter according to the instructions on the bottle may be helpful after you have removed the affected leaves.
Visit the Treewatch site on line - they're conducting a survey to see how far this infection has spread, so they'd like to hear from you about yours.
If you have any juniper trees or bushes nearby, check those for infection - usually presents with knobbly swellings on the branches; orange hornlike outgrowths can be seen in spring.

thankyou bamboo for your information on rust i have removed the infected leaves and am now in the process of burning them ,i will be visiting garden centre to buy said product once again thanks Ken

;-))