It's not expensive to "take legal action" via (what was) the Small Claims procedure (for claims up to �5000) you can do it all online now, see here;
https://www.moneyclaim.gov.uk/csmco2/index.jsp
The fee to start a claim is roughly 10% of the amount claimed, up to a maximum of �120, which may be added to what you are owed. Forms are available from www.hmcourts-service.gov.uk but for fixed cash debts, you can issue your claim online at www.moneyclaim.gov.uk.
The defendant has two weeks to respond after the court forwards the claim, and the ideal outcome is that the defendant does not contest the case, and pays up without you even needing to go to court.
But if the defendant disputes your claim, a hearing is necessary, and you could wait months to be allocated one � so consider whether you're prepared for the long-haul. The two parties present their cases to a judge in relatively informal surroundings, and another fee may be charged. The defendant is usually asked to pay such costs if you win, but not any solicitor's fees you incur.
For most small claims a solicitor is not necessary: to recover money owed for instance, you just need to prove the debt exists by way of invoices etc.