Contract

I have few questions regarding Contract you send over the email e.g when the client is living in another country.
1) Late payments: Is it legal to write on contract: 5% interest accrued (to be added every 7 days) if the payment is late more than 14 days. I read somewhere on internet, some freelance graphic designers add this to their contract not sure how it is in UK. Some clients, really delay payments even months and I think adding this anotation might speed up the process of getting paid.

2) Signature: Can I use my converted to vector signature and just copy/paste it on my contract and how client should sign the contract? Print it, scan it and send it back as .pdf ?

If you have any other answers that you think are important to include in this thread, please share it with me/us.
Thank you!