A system of Tiers (Tiers 1, 2 and 3) was introduced in England on 14th October relating to the Covid-19 outbreak. Each area of England is assigned to a particular Tier depending on the extent of the coronavirus infection in that area (mainly based on cases per 100,000 of population).
Different rules and guidance apply in Wales, Scotland and Northern Ireland.
Information on the rules that apply to each Tier can be found here. The document also shows which areas of England are within each Tier. At the time of writing (13th October), all of Devon is within the lowest Tier (Tier 1: medium risk).
A government poster showing the rules for Tier 1 can be found here.