The legality of saving life should not be compared to the illegality of concealing illegal immigrants in your lorry.
The lifeboatmen are not doing anything like the same thing as the lorry drivers who choose to bring in people who pay for their illegal journey.
Lorry drivers are in no physical danger and they are wellpaid for risking arrest. Lifeboatmen go out in all weathers, unpaid, risking their lives, to rescue "those in peril on the sea". Without that aid, the travellers whoever they are would not survive without their help. Leaving them to drown would be the equivallent of throwing them overboard and watching them disappear beneath the waves.
This is supposed to be a Christian country, but you don't have to profess Christianity to agree with what Jesus said, when jobsworths tried to trip him up by asking "“Is it lawful to heal on the Sabbath?” just so that they could accuse him of breaking the religious laws against working on the day of rest. "He said to them, “Which one of you who has a sheep, if it falls into a pit on the Sabbath, will not take hold of it and lift it out? Of how much more value is a man than a sheep! So it is lawful to do good on the Sabbath.”
It is lawful to save a life on any day of the week, and whoever's life is saved. Even murderers lives are not legally taken from them.