First: About calcium supplements, the blood needs a carefully adjusted amount of sodium, potassium, magnesium and calcium (and a few other minerals) in order for the cells to function and create movement. An example is why you get thirsty after eating a high-salt meal (rich in sodium). The body needs more water to thin out the concentration of sodium.
We carry almost 1 kg (= 2+ pounds) of calcium in the bones, but the concentration of calcium in the blood is very low (approx. 10 mg pr dl.) and even an increase to 15 mg/dl would cause very serious symptoms. If needed, calcium can be released from the bones, so the amount of calcium in the blood is fairly constant. If we go for years and decades with insufficient calcium intake, the bones can get weakened as they are drained for calcium. This is known as osteoporosis.
If we do not have this problem (insufficient calcium intake or diseases that drain the bones for calcium), supplements are just expensive and unnecessary (= unless your doctor say you need calcium, why take it?). If we take too much calcium, the kidneys may have a hard time getting rid of it (in order to maintain the blood calcium at approx. 10 mg/dl which is very important), which can cause kidney stones. If the kidneys are failing to get rid of all the calcium, it may gather up in the blood, which may cause high blood pressure and some say it may cause calcification in the arteries. That's the reason for an assumed increased risk of heart attacks.
Glucosamine is not such a supplement, and honestly I have never heard about it before. I can just quote my doctor, saying the only necessary supplement is omega-3 and during the winter, vitamin D (I live in Norway, maybe lack of sunlight is less of a problem in UK), unless your blood tests show that you lack certain minerals or vitamins. If you don't lack the supplement you are taking, the only "effect" is side effects, and essentially you are just making your urine more expensive (as the body just sends out unnecessary supplements that way).
Thank you for your informed reply. This is very common supplement in UK and is widely believed to promote healthy joint action by building preventing erosion and building connective tissue. I believe it is derived from crustaceans. It would be most widely taken by those with joint pain.