I must say I can't see a huge advantage in having Direct Access in a conventional ISA or a SIPP. Neither wrapper is remotely suitable for trading. Long-only, restricted market, Stamp Duty etc etc.
A possible exception: SIPP CFDS. GNI Touch and IG Markets both offer SIPPs in conjunction with synthetic Direct Access. You will need to be an Intermediate Customer though.
Whether you should even be trading in a pension plan is another matter. Personally I prefer to use Investment Trusts for my long-term savings. The pension is for avoiding poverty in old age, not getting rich ...