No, but you may be charged a non-return fee for the old router based on the following table:
V6: up to £100 per unit
Hub 3: up to £50 per unit
Hub 4: up to £75 per unit
BB Back-up Unit: up to £50 per unit
Wired Booster: up to £50 per unit
WiFi Booster: up to £50 per unit
Intelligent WiFi Pod: up to £50 per unit
VTV360: Up to £100 per unit