With a loss to the victim of £50k, the offence starts out as 'Category 3' within the 'Harm' part of the calculation used by judges. However if the effect on the victim is particularly detrimental it can be seen as a 'Category 2' offence.
If 'culpability' is seen as 'low' (e.g. because the fraud came about through an unplanned, opportunistic offence) a Category 3 offence would typically result in a sentence of around 6 months imprisonment (with a range that goes from a community order up to a year's imprisonment available to the judge). For a Category 2 offence the starting point sentence would be 18 months imprisonment (with an available range of 6 months to 3 years).
If 'culpability' is seen as 'medium' a Category 3 offence would have a starting point of 18 months (with a range of 6 months to 3 years). A Category 2 offence would have a starting point of 3 years (with a range of 18 months to 4 years).
If 'culpability' is seen as 'high' (e.g. because there had been an abuse of trust, as in when a financial adviser defrauds a client or where fraudulent activity had persisted over a long period) a Category 3 offence has a starting point of 3years (with a range of 18 months to 4 years), whereas a Category 2 offence has a starting point of 5 years (with a range of 3 to 6 years).
Summarised from the actual document which judges must refer to, here:
https://www.sentencingcouncil.org.uk/wp-content/uploads/Fraud-bribery-and-money-laundering-offences-Definitive-guideline2.pdf