Applying on 'Immigration Status Document'

Hello all

As background my wife got ILR in 2010 on marraige basis and I am UK born/Passport. Her ILR was issued on an 'Immigration Status Document' as her Travel Document expired in 2009. She is Tibetan and was traveling on a 1 year or 1 trip Nepali Travel Document.

Can we apply for Naturalisation with this and the original Travel Document or do I need to change it on to a Biometric Residency Card first please?

In addition, trying to book an english test is proving difficult given the colleges are asking for passports or biometric residency cards as proof. If I was going to swap the ILR from the Immigration Status Document to one of these cards would I use form BRP or NTL please?

Thank you in advance

I presume requesting an ILR on Biometric would be more expensive and time consuming than requesting a Nepali Passport. So personally I would just request a Nepali Passport for B1 tests etc (should not take more than four weeks) and use that along with ILR documents for Naturalisation application.