Contracts don't lapse; it's just the min. term that expires. That's why, generally, you continue paying the same under the existing contract (subject to its terms on price rises). Hence it is often advantageous to to lock in to a new min term under a new contract in exchange for a lower price.
1999: Freeserve 48K Dial-Up => 2005: Wanadoo 1 Meg BB => 2007: Orange 2 Meg BB => 2008: Orange 8 Meg LLU => 2010: Orange 16 Meg LLU => 2011: Orange 20 Meg WBC