If you're not sure where to start, an ISO 400 colour negative film is the safest choice in Britain: it handles overcast days and evening shots, though you will likely need a flash for indoor scenes. ISO 100 and 200 stocks are finer grained and better suited to bright, sunny days or tripod work.
Choose the look as well as the speed. Ektar 100 offers fine grain and saturated colour for landscapes and detail, while portrait focused colour stocks tend to favour gentler contrast and natural skin tones.
Most black and white film is developed differently to colour (though some, like Ilford XP2, use the C41 process): check the process before you buy. We run C41, traditional B&W chemistry for Tri X and T Max, and E6 for Ektachrome slide film.
Compare the price and exposure count rather than assuming a longer roll or a pack is always cheaper. Refrigeration can help preserve unexposed film, but follow the expiry and storage guidance and let sealed film warm to room temperature before loading.