I have quite a lot of varicose/spider veins in my legs. should i be co corned about very painful ones at the front of my knee? tender to touch gently

Yes, pain: in a superficial venous varicosity could mean thrombosis or skin breakdown. Or it could be something else, b/c such severe pain in front of knee is a bit unusual for varicose vein. Show it to your doctor to be sure.

Types of veins.: Both spider and varicose veins can be treated very successfully and cosmetically very acceptably. You should see a vein specialist for a full venous evaluation including a venous ultrasound. Varicose veins are usually due to refluxing saphenous vein valves and spider veins have many causes. Painful veins may have clots in them and should be evaluated.