These data are taken from the website of an UK based agency. It would give an idea how much they are charging for Spanish translation. It seems this is not a big agency. May be an one man agency. But the information is useful in deciding your rates in UK.
Translation: fees range from £60 to £120 per 1000 words
Generally, no distinction is made in price terms between translations from English into Spanish or from Spanish into English.
Interpreting: Rates for business, technical, legal and community interpreting are £175 per half day and £300 for a full day.
Voice-overs: these are charged at a flat rate of £500 per recording session (no more than one normal working day).
Bilingual Secretarial Services: billed at £20 per hour (subject to minimum charge).
Audio Transcription: as a general guide, rate for transcription (including translation) is £120 per 1000 words.
Spanish tuition: our rate is £30 per hour for private individuals and £40 per hour for companies, exclusive of travelling costs and time, if applicable.