Citizens of United Kingdom can enter Indonesia visa free for up to 30 Days. You only need to purchase a visa if you intend to travel to Indonesia for longer than 30 Days.
If you are entering Indonesia for less than 30 days, citizens of certain countries can pass visa free through any of the following ports:
Airports: Hang Nadim, Batam; Juanda, Surabaya; Kualanamu, Medan; I Gusti Ngurah Rai, Denpasar; Soekarno-Hatta, Banten
Seaports: Bandar Bentan Telani Lagoi, Tanjung Uban; Bandar Seri Udana Lobam, Tanjung Uban; Batam Center in Batam; Citra Tri Tunas, Batam; Marina Teluk Senimba, Batam; Nongsa Terminal Bahari, Batam; Sekupang, Batam; SriBintan Pura, Tanjung Pinang; Tanjung Balai Karimun, Tanjung Balai Karimun
Your passport must be valid for at least 6 months from the date of entry into Indonesia and you must present evidence of onward or return tickets.