In order to try and resolve the dispute without having to pursue court action, a formal letter before action should be drafted and sent, to demand payment within 14 days and say that if they do not pay you, you will issue county court proceedings against them.
See attached template as an example of what to say. Please let me know if you cannot see the letter which I have uploaded. You will need to tailor this letter to your situation. The pre action protocol confirms you should send the letter to give the other party a chance to avoid court action and to pay you. The courts encourage compliance with the protocol as it can result in a resolution without having to involve the court. You may also want to threaten a report to Trading Standards (who can be contacted via this site: https://ssl.datamotion.com/form.aspx?co=3438&frm=general&to=flare.fromforms).
If you decided to issue a claim, you would then need to register at the money claim online site (http://www.moneyclaim.gov.uk/web/mcol/welcome) so that you are ready to issue the claim in the event they dispute the claim and do not pay you.
The website is very user-friendly and you would not need a lawyer to use the money claim site.
A hearing may be necessary if the court thinks that oral evidence is required to dispose of the case. The court will then issue the claim and they will send you "notice of issue". The papers are served on the defendant who then has 14 days to acknowledge the claim - they do this by filling out an acknowledgment of service and they post it to the court.
They indicate their intention when they do this, i.e. whether they admit the claim in full or partly, or if they deny the claim. If they want to defend the claim then their defence is due by 28 days from the date the court served them with the papers.
The central court processing centre then sends the claim to the defendant's home county court for case management and directions - the directions will give a list of dates which you both must comply with.
The court should offer you mediation to encourage you to resolve the dispute early on - though for mediation to work both parties have to agree to participate.
If there is no settlement then the claim will be dealt with at a final hearing which takes anything from 9 to 12 months from when you start the claim - longer if the claim is of higher value. You can pursue the claim yourself or use a law firm.
For the hearing you can use an advocate if you wish, though it's not compulsory. I have details of law firms and advocacy agencies if you would like those. Though in a small claim you won't be able to recover their charges from your opponent. A small claims hearing is easy to deals with- it's quite informal and no lawyer is required.
Claims between £10,000 and £25,000 are subject to fixed costs only so if you lose then the risk is minimal. Further, the money claim website allows you to sue for an amount up to £100,000.
You would claim the sum for the loss, the court issue fee (details of the money claim fees are listed here at page 5: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1056804/EX50_web_0222.pdf) and court interest which is 8% calculated on a daily rate from the date of loss to date of court judgment.
So for example if you were owed £10,000, interest would be £2.20 per day, which you can also claim. The site allows you to calculate the interest and add it to the claim. If a hearing is required then there is a fee for this too - see page 7 of the previous link for details. Again, that fee is recoverable if you win.
If you are on a low income or have low savings (or in receipt of benefits), you can ask the court for a fee remission so you do not have to pay the court issue fee.
If you do qualify for a fee exemption, you cannot use the money claim online site - instead you would need the paper N1 claim form (let me know if you would like a copy) as well as the EX160 fee exemption form which goes with the N1 claim form - then posted to court.