If you own an older car then there may come a time when the cost of the repairs outweigh the value of the car. If this is the case then you have to make the choice as to if you want to risk spending the money on it and hope that it will last you for another few years or whether you cut your losses and start again. If you can only afford to buy another cheap car, less than £1500 then you may find that the types of vehicles that you can buy within your budget will need work doing anyway, or may not last very long. This is often a cycle that may people get into and it can be hard to get out of it.
If possibly try and save a bit of money every month so when you do some to sell your car you have an additional amount saved to put towards a new one, hopefully allowing you to buy something better.