Building experience is an important first step into many international development roles. In many respects, experience is as important as qualifications. A Master's may be useful to progress your career later, but when you are starting out it is essential to build experience. Volunteering is a good starting place. Research NGOs and approach them directly. Try to get some overseas experience. There are plenty of organisations that can help with this, but costs will vary considerably.
Search for overseas volunteering opportunities, but don't forget to think about useful opportunities in Brighton while you are here:
There are thousands of NGOs doing niche work that can offer invaluable work experience opportunities. Use these resources to research NGOs working in areas you are interested in (geographically or thematically):