First of all I would like to thank you for your letter. I'm glad that you remember me and you don't forget about our friendship.
I was really shocked when I found out that you're inviting me to England ! That would make my dreams come true.. I've always wanted to visit this beautiful and interesting country. Unfortunately, I can't come. Despite the fact that I really want to do so, it's not possible ! Thank you for invitation, anyway. One of the main reasons why I can't come is the fact that I've already got plans, and my parents booked for holiday in Greece. We can't deny it now. It's too late ! I'm really sorry, I wish I could come. You know what? I'm free on second month. I mean August. If you could rearrange the invitation on August I could come ! Please, think about it and tell me, because it's very important for me.
I gotta go now. I'll be waiting for your answer. I'm sending greetings to your parents. I hope it's possible for you to invite me on second month of our holiday.
(Imiona sama wymyslilam, wstaw tam co chcesz, licze na punkty, hihihi ;D)