Immigration officers are tough cookies, hun.

I wouldnt suggest lying to one no matter the circumstances. If they find out you're lying even at a later date, they can revoke your visa and have you deported to your country of nationality.



If you're wanting to study, I'd suggest a student visa. They really aren't all that expensive and if you've already got a letter from the school, you should be fine.

I'm fairly sure most EU student visas are for multiple entry...

 

My guess is that you are non visa national.You dont need visa prior to your entry.If this is the case you dont need student or any other visa to come and study few weeks in the UK.
Where do you come from?

 

Here@
"You asked if a national of Hong Kong (SAR Passports) needs a visa to come to the UK as a student for six months or less.

No, you do not need a visa.

On arrival in the UK you must satisfy an immigration officer that you qualify for entry to the United Kingdom as a student for six months or less under the Immigration Rules.

Students
Please note that if you are allowed to enter the UK as a student for up to six months, you will not be allowed to extend your stay unless you arrived with a student or prospective student visa, or are studying on a course at degree level or higher. The Home Office will charge you a fee for applying to extend your stay."

Now, if you want to leave UK have a holiday and come back may cause a problem.
You maybe better off getting multiple entry visitors or student visa.

 

3 months for you in Spain.