If you're sending to Richard Griffiths, for God's sake use British stamps on your SASE! x3 If you use any other stamps, IRC, money or nothing at all you'll get one of his "famous angry letters" (but usually no autographs). But if that's what you want, go ahead, hahah ^^

You can only use US stamps if you are sending to the UK. For your SASE you have to use UK stamps. Alternatives is you can send IRC or money. But with Richard Griffiths I would not send irc's or money.

I want to send to Richard Griffiths the UK and I'm from the US.

What I'm sending:
LOR, index card, HP page from newspaper, & SASE

Can I just use US stamps on both envelopes?