Background: Adults with intellectual disabilities and/or autism are often excluded from participating in health and healthcare research. Understanding study information, which is an important aspect of demonstrating capacity to give informed consent, can be a particular challenge. This study surveyed clinical researchers to discover: (i) their experiences of assessing mental capacity for research; (ii) what methods they used to facilitate the inclusion of adults with intellectual disabilities and/or autism; and (iii) their views about a proposal to develop new resources to facilitate mental capacity judgements with adults with intellectual disabilities and/or autism for informed consent for research. Methods: Clinical researchers in North East England who conduct research with NHS patients with intellectual disabilities and/or autism were invited to participate in a 22-item self-completed semi-structured questionnaire survey, either online or on paper. Results: Twenty-one clinicians completed the survey (response rate 30.4%). Participants reported on 18 research studies which included people with intellectual disabilities and/or autism. In many studies people who lacked capacity to give informed consent were excluded, and often shortcuts were taken in judging capacity. Limited adaptations to support capacity were used. Respondents welcomed the proposal of developing assistive resources that could support capacity judgements and informed consent to research. Conclusions: To improve access to research for people with intellectual disabilities and/or autism, researchers need robust methods to facilitate informed consent and mental capacity judgements. Future research should determine which assistive resources show potential to support informed consent and capacity decisions, and whether such resources could improve inclusion in research.