What’s the most likely cause when the brake pedal feels spongy?

Explanation: If you operate the brakes when air is in the hydraulic system, they'll have a spongy feel and braking efficiency will be reduced. This is because the air in the system is being compressed as you brake; hydraulic brake fluid alone can't be compressed. If you notice there's a fault with your brakes, have them checked as soon as possible. Don't drive with faulty brakes.

Category: Band 2 traffic signs and signals

References: The Official DVSA Guide to Driving: Section 14