Immigration Officers are not allocated a duty at a particular channel of the Primary Arrivals Control at Heathrow airport; they serve the Border Control as a whole. Shift managers decide how many of the available staff should work in the EU or non-EU channels at any particular time in order to deal with approaching passengers as quickly and effectively as possible. The only constraint is that one officer must be on duty in each channel at all times when flights are landing. This flexibility makes the best use of available resources.