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2. You can do the same thing if you want to insert a link to another web page - just paste the full address of the external page into your post.
You will probably not (never say never in law) be covered by section 70 of the Consumer Credit Act (1974). This is the section that makes Credit Cards 'jointly and severally' liable for purchases over £100. In order for the section to apply there must be a 'DCS' arrangement. A (D)ebtor has an arrangement woth the Creditor (Credit Card), the (C)reditor has a relationship with the (S)upplier (the Seller accepts payment by CC), and finally the (S)upplier has a relationship with the Debtor (with whom the contract has been formed). In the case of paypal there is no relationship between the Creditor and the Supplier. The Creditor has a relationship with Paypal, and Paypal has the relationship with the Supplier. Under s.70 CCA the Credit Card is only responsible if 'Paypal' fail to deliver the service to the Debtor (you), i.e. Paypal take too much money or fail to pass it on to the supplier. Summary - Paypal break the DCS link stopping s.70 cover. They will fob you off to the CC company, knowing full well (IMO) that you are not covered by statute. However you may be covered by the CC's contractual guarantees (such as online fraud protection).