The key word in the question is 'contingency'. This means changing your routing without an ATC clearance...

Imagine being on one of many NAT parallel tracks, with aircraft stacked 1000 ft apart vertically above and below you. If you need to divert, then doing so safely will require obtaining a degree of separation from surrounding aircraft. In this event:

1. Separate laterally: turn left or right by at least 30° until 5 NM off track and then parallel. Minimise descent during this phase.

2. Separate vertically. If you need to descend below NAT HLA, now descend to FL280. Otherwise, if in RVSM airspace then split levels by 500 ft.

Note: An simple way to detect correct and incorrect answers is to remember:

1. Contingency scenarios climb or descent: 500 ft
2. Weather avoidance climb or descent: 300 ft

NORTH ATLANTIC OPERATIONS AND AIRSPACE MANUAL — CHAPTER 13
13.2 GENERAL PROCEDURES

13.2.1 If an aircraft is unable to continue the flight in accordance with its ATC clearance, a revised clearance shall be obtained, whenever possible, prior to initiating any action. If prior clearance cannot be obtained, the following contingency procedures should be employed until a revised clearance is received:

a) leave the cleared route or track by initially turning at least 30 degrees to the right or to the left, in order to intercept and maintain a parallel, same direction track or route offset 9.3 km (5.0 NM). The direction of the turn should be based on one or more of the following:

1) aircraft position relative to any organized track or route system,
2) the direction of flights and flight levels allocated on adjacent tracks,
3) the direction to an alternate airport;
4) any strategic lateral offset being flown, and
5) terrain clearance