It really should make no difference if you go directly to a landlord or through an agency, both should do a credit check on you. Individual landlord's tend not to charge for this whereas an agency usually does.
If you come back with a poor credit score then you could offer to pay a larger deposit or offer a guarantor (who would also have to pass the credit check).
A reference will usually be taken from your last landlord, and this may help you, though a poor credit score will probably override this.
There's a glut of properties on the rental market at present and this may work in your favour as the landlord/agent may be less choosy.
As a landlord, I think �150 is well over the top for something which only costs about �30.