Depending on your field of interest, timeframe, and career objectives, a degree plus a DipGrad could suit your plans better than a double degree.
For example, if you do your first degree consisting of 20 papers at 18 points each with a major in Microbiology (MICR), and you also want the equivalent of a major in English, you could do a second degree, majoring in English. Since you can cross-credit 1 year’s worth of work from your first degree, you may need to do only 13 papers for the second degree. Some of these 13 papers would be needed to satisfy the English major subject requirement but the remainder may be chosen according to your interests.
But you could just do the 7 English papers (with 4 at 300-level) in addition to your first degree, to gain a DipGrad endorsed in English. This means that instead of spending 5 years doing 33 papers to gain a BSc in Microbiology and a BA in English, you would spend 4 years doing 27 papers to gain a BSc in MICR and a DipGrad endorsed in ENGL.