Ah this great country where you can beat the crap out of someone and get a telling off but get jail time for financial matters like this
I agree.
Jail is expensive and should be used only where it will be of benefit to the public because they would be at severe risk if the person were free in society. With financial crimes it's risk-reward. If you think the amount you can gain is greater than the amount of time you'd spend in prison then there's an incentive to commit that crime.
Say, for example, that someone is convicted of a crime that gains them a few hundred thousand pounds and is difficult to recover, for which the defendant would receive a couple of years in prison. If they work out that the risk/reward is equivalent to £100k p.a. then they might consider it worth the risk. After all, few jobs would earn you that much.
Instead, let's say the penalty would be monetary and double the amount the person stole, and/or has to be 'worked off' with community service at a rate comparable to minimum wage per hour. That makes it far less appealing. The for repeat offenders it can either increase to three/four times the amount and/or in exceptional repeat offenders mixed in with jail time again comparable to the amount stolen (say, done on a average wage pro-rata basis so say you stole c.£35k you'd get a year in prison, £70k two years etc.)