After you have worked for 12 calendar weeks in the same role with the same hirer you will be entitled to equal treatment irrespective of your working pattern (e.g. full time or part time) and irrespective of which or how many agencies supplied you to do the same role at the hirer.
Any time worked during a week will be counted as ‘one week’ for the purposes of calculating the qualifying period even if you have only worked a few hours in a week. For example – if you start an assignment on the Saturday, any work done up to and including the following Friday will be counted as one week towards the qualifying period.
A new qualifying period will begin only if a new assignment with the same hirer is substantively different (and that does not mean simply changing a job title; it will mean looking at the work and duties performed), or if there is a break of more than six weeks between assignments in the same role (except in certain limited circumstances).