To obtain the RTB1 form, you will need to visit the right section of the High Peak Council's website. Unfortunately, I couldn't find a direct link to the RTB1 form specifically, but if you are looking to buy your council house, the relevant information can typically be found under the 'Buying your council house' section.
For your convenience, you can explore the information related to buying your council house here. If you still need assistance, consider reaching out to the council directly for the form.