Getting party wall consent is a legal requirement under the Party Walls Act 1996. While there are no enforcement provisions under the Act, the adjoining owner can get an injunction stopping you doing work until a Party Wall Agreement is reached - so if you start without an agreement, then your work could be halted mid-stream, which would probably add more time and cost than getting an agreement in the first place. Also, part of a party wall agreement is usually a schedule of condition, which documents the state of the adjacent property prior to the works. Without this, there is a risk that the adjoining property owner could claim that existing damage is actually due to your works and ask you to repair. Without the schedule of condition you could have difficulty proving that it wasn't due to your works. Not having a party wall agreement to save some money strikes me as a very risky thing to do! (You need to give notice between 2 months and a year before starting work)
Andrzej Kowalski ● 707d