Disbursements are expenses that the solicitor has to pay for in excess of their legal costs.
They are generally office recharges for things such as photocopying, postage charges stationery used and bank charges such as telegraphic transfer costs.
If you are purchasing a property, you have to request that your solicitor orders searches on your behalf. There are many types of searches and your solicitor knows which ones will be applicable as necessary to match your property purchase. There are varying fee amounts charged for the different searches available and your solicitor will normally request you pay a deposit before any work is done on your case as they will be loathe to expose themselves to any risk or spend money from their own funds.
If you were able to dig deep, which you won’t be able to do, you’d probably find that the recharges are being hiked up. For instance, photocopying costs applied of £15 may be applied when your actual consumption of paperwork copied on your case was only equating to £3.40. So your solicitor is making up more money on top of their standard fees by doing this. There’s nothing you can do about it and it likely goes on in every solicitor practice in the UK.