You can draft one online, but in order to be valid has to be
signed by the testator or by someone else in his presence and at his direction, in the presence of 2 or more witnesses who then attest and sign the will in the presence of the testator. (S9 Wills Act 1837)
Although I agree to some extent with TonyV about getting one drawn up professionally, my view on this is that this is because there are less likely to be construction problems. Having a professional drawn will makes no difference to the likelihood of dispute - it just may affect the outcome!
Yes you can. I think "Which" do a guide to making your own Will and you can get a will pack from stationers. So long as you sign it in the presence of 2 witnesses (who must NOT be beneficiaries or married to beneficiaries) and they then sign it, should be fine.
dzug2 said "It would be perfectly legal if done properly"
How does someone decide it's done properly if not qualified?
Anna - Barmaid is correct about the construction (wording) which is what I guess I really meant. But there are other considerations to make e.g. what happens if you out live one of your siblings and don't ammend your will? Do you have grandchildren or son / daughter in law that their share would go to?
I am not legally qualified, and only speak from experience.