My advice would be to speak to JTL Training, the C&G 6129 can still, I believe, be APL'ed (Attained Prior Learning) over against the 6189 NVQ Level 2, so no college side, you will just need to obtain the on site evidence & be observed a couple of times, it can be complete quickly if you have access to the right types of work, are up to the required skill level & prepared to put the written work in to complete the portfolio.
But you might want to do this quickly as the Plumbing Qualifications are changing real soon ( I thing the deadline is June for JTL) Training centres may not be able to offer this as they move over to the new Plumbing standard 9189, no level 2 only level 3 over 3.5 to 4 years, with gas or other fuels or renewables in the last 8-12 months & end point trade assessments when you finish, to name just a few of the changes.
P.S. The portfolio is actually easier to complete if you do new bathrooms so long as they are not just straight swops with little pipework you don't need heating work but it can be used so long as you are installing new rads & pipework or the like. You certainly don't need gas work for Level 2 or 3.
Hope that is some help.